Oxidation Of 1a Research Articles

Copper-Catalyzed Ligand-Controlled Selective Borocarbonylation of α-Substituted Styrenes Toward β-Boryl Aldehydes and Cyclopropyl Boronate Esters

Copper-Catalyzed Ligand-Controlled Selective Borocarbonylation of α-Substituted Styrenes Toward β-Boryl Aldehydes and Cyclopropyl Boronate Esters

Tropane-Based Dispirocyclic Oxiranes and Spirocyclic Ketones

AbstractThe Prilezhaev epoxidation of N-Boc-protected 3-cyclobutylidenetropane 1a affords a 1:2 mixture of compounds 2a and 2b, in which tropane and cyclobutane fragments are spiro-connected to the oxirane ring in endo- and exo-fashion, respectively. The exo-isomer 2b is obtained in 89% yield and 97% selectivity via the dioxirane oxidation of 1a. BF3-catalyzed isomerization of exo-oxirane 2b results in a 1:1 mixture of the spirocyclic ketones endo 3a and exo 3b containing spiro-connected tropane and cyclopentanone rings, while endo-epoxide 2a gives exclusively endo-ketone 3a. Prilezhaev and dioxirane epoxidations of N-Boc-protected 3-cyclopropylidenetropane 1b affords a mixture of endo- and exo-oxiranes 2c and 2d. Compounds 2c and 2d are not isolated in individual forms since they isomerize into a mixture of spirocyclic ketones endo 3c and exo 3d. Removal of the Boc groups from ketones 3a–d gives the corresponding hydrochlorides of aminoketones 4a–d in quantitative yields. Quantum chemical calculations predict that the rearrangement of endo-epoxides into the corresponding endo-ketones involving BF3-containing intermediates has by 4.4–7.9 kcal/mol lower activation barriers than the respective conversion of the exo-epoxides into exo-ketones. The cyclopropyl-containing dispiroepoxides 2c and 2d are predicted to interconvert faster into the corresponding ketones compared to their less strained cyclobutyl counterparts 2a and 2b.

Coligand modulated oxidative O-demethylation of a methyl ether appended tetradentate N-ligand in Co(ii) complexes.

Two Co(ii) complexes of the formula CoLOMeX2 (X = Cl- (1a); X = I- (1b)), where LOMe is 2-methoxy-N,N-bis(pyridin-2-ylmethyl) aniline, were synthesized and their structure, spectra and reactivity were studied. Upon oxidation of 1a and 1b, the ligand LOMe undergoes demethylation at the metal centre resulting in the formation of Co(iii) complexes with modified phenoxide ligands. This is the very first example of oxidative O-demethylation reported at a Co(ii) centre. The oxidative behaviour exhibits a striking dependence on the nature of coligands coordinated to the metal centre. The Co(ii) complex 1a with stronger chloro coligands requires a strong oxidising agent like t-BuOOH for oxidative demethylation and the subsequent formation of a mononuclear Co(iii) complex with a demethylated ligand, CoLO-Cl2 (2). On the other hand, complex 1b with weaker iodo coligands undergoes oxidation in the presence of the weak oxidant O2 to form a dihydroxo bridged binuclear Co(iii) complex [Co2(LO-)2(OH)2]2+ (3) with modified phenoxide ligands. The oxidation of 1b to 3 is monitored and the intermediate Co(ii) iodo aqua complex [CoLOMeI(H2O)]+ and Co(ii) diaqua complex [CoLOMe(H2O)2]2+ are isolated and characterised.

A New Potential Contrast Agent for Magnetic Resonance Imaging: Iron Oxide-4A Nanocomposite

Background: Magnetic resonance imaging (MRI) contrast agents have an important role to differentiate healthy and diseased tissues. Access and design new contrast agents for the optimal use of MRI are necessary. This study aims to evaluate iron oxide–4A nanocomposite ability to act as a magnetic resonance imaging contrast agent.Materials and Methods: Iron oxide–4A nanocomposite (F4A) was synthesized. MTT assay was used to consider the nanocomposite safety for cell culture. The T1 and T2 relaxation times were measured using a 1.5 Tesla clinical MRI scanner. Then the corresponding relaxivities were determined.Results: The average particle diameter of the nanocomposite was 50 to 100 nm based on scanning electron microscope (SEM) image. A linear relationship between relaxation rates and the Fe concentration of the nanocomposite was obtained. The T1 and T2 relaxivities of the nanocomposite were calculated 5.413 and 1092.1 mM-1.s-1, respectively which led to the T2/T1 relaxivity ratioof 201.75.Conclusion: The high T2/T1 relaxivity ratio of the iron oxide–4A nanocomposite confirms it’s potential to act as a T2 contrast agent.

The First Naked Bismuth-Chalcogen Metal Carbonyl Clusters: Extraordinary Nucleophilicity of the Bi Atom and Semiconducting Characteristics.

Mixed bismuth-chalcogen-iron clusters [{EFe3(CO)9}Bi]- [E = Te (1a) or Se (1b)] were produced via the reduction of BiCl3 with [EFe3(CO)9]2- under mild conditions. X-ray analysis showed that both clusters 1a and 1b had a square-pyramidal geometry, where the naked Bi and chalcogen both adopted a distorted trigonal-pyramidal configuration with a stereoactive lone pair. Complexes 1a and 1b can be further functionalized by methylation and metalation, which permits the nucleophilicity of the 6s/5s and 6s/4s lone pairs to be compared. In the metalation, the 6s pair of the Bi atom in 1a and 1b had an extraordinary nucleophilicity toward the unsaturated Cr(CO)5 fragment, even in the presence of the more chemically active 5s or 4s pair, whereas in the case of methylation, only the 4s pair of Se could be selectively alkylated. Upon oxidation of 1a and 1b with suitable oxidizing agents, NaBiO3 or K2SeO3, Bi-E bonded tetrahedral complexes [{EFe2(CO)6}Bi]- [E = Te (4a) or Se (4b)] were formed by the elimination of one Fe(CO)3 vertex. X-ray photoelectron spectroscopy, X-ray absorption near-edge structure, and density functional theory (DFT) calculations showed that all of the Bi atoms in these complexes had oxidation states close to +1. Due to the electropositive character of the Bi atom, pronounced induced Bi···E inter- and intramolecular interactions were evident in 1a (1b), 4a (4b), and the metalated 3a (3b), where their linear-like ···Bi···E··· or zigzag-like ···Bi-E··· (E = Te or Se) chain or the Bi···E···E···Bi (E = Te or Se) dimeric chain can further expand into the two-dimensional network via nonclassical C-H···O(carbonyl) interactions, supported by noncovalent interaction index and DFT calculations. These positively charged Bi-induced Bi···E (E = Te or Se) and carbonyl-aided weak interactions can facilitate efficient electron transport within these ternary Bi-E-Fe or quaternary Bi-E-Fe-Cr cluster-based frameworks, resulting in semiconducting behavior with surprising ultranarrow energy gaps of 1.01-1.21 eV.

A New Potential Contrast Agent for Magnetic Resonance Imaging: Iron Oxide-4A Nanocomposite

Magnetic resonance imaging (MRI) contrast agents have an important role to differentiate healthy and diseased tissues. Access and design new contrast agents for the optimal use of MRI are necessary. This study aims to evaluate iron oxide-4A nanocomposite ability to act as a magnetic resonance imaging contrast agent. Iron oxide-4A nanocomposite (F4A) was synthesized. MTT assay was used to consider the nanocomposite safety for cell culture. The T1 and T2 relaxation times were measured using a 1.5 Tesla clinical MRI scanner. Then the corresponding relaxivities were determined. The average particle diameter of the nanocomposite was 50 to 100 nm based on scanning electron microscope (SEM) image. A linear relationship between relaxation rates and the Fe concentration of the nanocomposite was obtained. The T1 and T2 relaxivities of the nanocomposite were calculated 5.413 and 1092.1 mM-1.s-1, respectively which led to the T2/T1 relaxivity ratio of 201.75. The high T2/T1 relaxivity ratio of the iron oxide-4A nanocomposite confirms it's potential to act as a T2 contrast agent.

Synthesis and combined properties of novel fluorinated cationic surfactants derived from hexafluoropropylene dimer

Three novel fluorinated cationic surfactants were prepared by adopting perfluoro-2-methyl-2-pentene as raw substrate. The as-obtained fluorinated cationic surfactants exhibited excellent surface properties, all of them can reduce the surface tension of water to below 20.00mN/m at the critical micelle concentrations (CMC). The incorporation of SDS, AOS, APG or LAB into 2-(4-(3,3,4,4,5,5,5-heptafluoro-2,2-bis(trifluoromethyl)pentyl)benzamido)-N,N-dimethylethana-mine oxide 4a could generate much lower CMC and surface tension value at the CMC than individual 4a. Especially, the surface tension values of that combined APG/4a can be reduced to 17.31mN/m. The excellent surface activities and their remarkable compatibility to various types of hydrocarbon surfactants make them as sustainable alternatives to PFOA (perfluorooctanoic acid, C7F15CO2H) and PFOS (perfluorooctane sulphonate, C8F17SO3X, with X=K, Na, H).

Autoxidation of Heterocyclic Aminals.

The autoxidation reactions of 2-acyl-2,3-dihydroquinazolin-4(1H)-ones 4a and 5a and 2,2′-bis(dihydroquinazolinone) 6a are described. These reactions generate aminyl radicals that undergo β-C–C cleavage, and subsequent reactions of the resulting C-based radicals with O2 lead to diverse products with good selectivity, depending on the structure of the substrate. Oxidation of 4a, in which the 2-acyl group is part of a cyclic acenaphthenone unit, yields a heterocyclic C-hydroperoxylaminal via 1,2-acyl migration. Oxidation of 5a, which contains a 2-acetyl group, yields peracetic acid and a quinazolinone product. Oxidation of 6a forms a bis(quinazolinone) by net dehydrogenation.

ChemInform Abstract: Reaction of 2H‐Azirine‐Phosphine Oxides and ‐Phosphonates with Enolates Derived from β‐Keto Esters.

Cyclopenta[b]-pyrrole-2-phosphine oxides 4a and -phosphonates 4b,c are generated by the addition of cyclic enolates derived from ethyl 2-oxo-cyclopentanecarboxylate 2 to phosphorated 2H-azirines 1. However, the addition of enolate derived from acyclic 2-oxo-butanoate 10 to 2H-azirine phosphine oxide 1 led to vinylogous N-acyl-α-aminoalkyl phosphine oxides 12, involving the carbonyl group and the Cα of the keto ester 10. Ring closure of vinylogous derivative 12 in the presence of base afforded pyrrole-2-phosphine oxide 11. The addition of enolates derived from indenone-carboxylate 15 to 2H-azirines 1 led to the formation of functionalized N-substituted 1H-benzo[d]azepine derivatives 17.

Mononuclear Iron‐(hydro/semi)quinonate Complexes Featuring Neutral and Charged Scorpionates: Synthetic Models of Intermediates in the Hydroquinone Dioxygenase Mechanism

Neutral and anionic scorpionate ligands have been employed to generate active‐site models of hydroquinone dioxygenases (HQDOs). While the nonheme Fe center in nearly all HQDOs is coordinated to one Asp (or Glu) and two His residues, 1,2‐gentisate dioxygenase (GDO) is unique in featuring a three His triad instead. A synthetic GDO model was therefore prepared with the neutral tris(4,5‐diphenyl‐1‐methylimidazol‐2‐yl)phosphine (Ph2TIP) ligand. The gentisate substrate was mimicked with the bidentate ligand 2‐(1‐methylbenzimidazol‐2‐yl)hydroquinonate (BIHQ). X‐ray diffraction analysis of the resulting complex, [Fe(Ph2TIP)(BIHQ)]OTf (1a), revealed a distorted square‐pyramidal geometry. Structural and electrochemical data collected for 1a were compared to those previously reported for [Fe(Ph2Tp)(BIHQ)] (1b), which features an anionic hydridotris(3,5‐diphenylpyrazol‐1‐yl)borate (Ph2Tp) ligand. Oxidation of 1a and 1b provides the corresponding FeIII complexes (2a/2b) and the crystal structure of 2b is reported. Both complexes undergo reversible deprotonation to yield the brown chromophores, 3a and 3b. Detailed studies of 3a and 3b with spectroscopic (UV/Vis absorption, EPR, resonance Raman) and computational methods determined that each complex consists of a high‐spin FeII center ferromagnetically coupled to a p‐semiquinonate radical (BISQ). The (de)protonation‐induced valence tautomerization described here resembles key steps in the putative HQDO mechanism.

Reaction of 2H-Azirine-Phosphine Oxides and -Phosphonates with Enolates Derived from β-Keto Esters.

Cyclopenta[b]-pyrrole-2-phosphine oxides 4a and -phosphonates 4b,c are generated by the addition of cyclic enolates derived from ethyl 2-oxo-cyclopentanecarboxylate 2 to phosphorated 2H-azirines 1. However, the addition of enolate derived from acyclic 2-oxo-butanoate 10 to 2H-azirine phosphine oxide 1 led to vinylogous N-acyl-α-aminoalkyl phosphine oxides 12, involving the carbonyl group and the Cα of the keto ester 10. Ring closure of vinylogous derivative 12 in the presence of base afforded pyrrole-2-phosphine oxide 11. The addition of enolates derived from indenone-carboxylate 15 to 2H-azirines 1 led to the formation of functionalized N-substituted 1H-benzo[d]azepine derivatives 17.

One‐pot Synthesis of 1,2,3,4‐Tetrahydropyrimidin‐2(1H)‐thione Derivatives and their Biological Activity

2‐Thioxo/oxo‐1,2,3,4‐tetrahydropyrimidine‐5‐carboxylate derivatives 2a, 2b, 2c, 2d were prepared by the reaction of ethyl acetoacetate and thiourea or urea with aldehydes using NH4Cl as a catalyst. Compounds 2a and 2c reacted with mono and bihalogenated compounds such as ethyl iodide, chloroacetonitrile, epichlorohydrin, acetyl chloride, ethyl bromoacetate, chloroacetic acid, chloroacetylchloride, and/or oxalyl chloride to afford compounds 3, 4a, 4b, 5, 6a, 6b, 7, 8, 9 and 10, respectively. Compounds 2a, 2c, and 7 were allowed to react with p‐fluorobenzaldehyde to yield the corresponding products 11a, 11b, and 12, respectively. Oxidation of 2a and 2c gave 2b, 13a, 13b, 14, 15, 16 dependent on the oxidizing agent used. Vilsmeiere‐Haack formylation of 2a and 2b with POCl3/DMF afforded 17a and 17b. Chlorination of 2b and 2d gave the chlorinated derivative 18a and 18b, which reacted with thiourea to give thioureidopyrimidine 19a and 19b. Reactions of 2a with hydrazine monohydrate, semicarbazide hydrochloride, and sodium hydroxide gave compounds 20, 21, 22, respectively. The cytotoxicity and in vitro anticancer evaluation of some prepared compounds have been assessed against two different human tumor cell lines including breast adenocarcinoma MCF‐7 and human hepatocellular carcinoma HepG2. Antimicrobial and antioxidant activities of some compounds were investigated. The newly synthesized compounds were characterized by IR, 1H‐NMR, 13C‐NMR, and mass spectral data.

Bimetallic nickel complexes supported by 2,5-bis(phosphine)-1,4-hydroquinonate ligands. Structural, electrochemical and theoretical investigations

The coordination chemistries of several 2,5-bis(phosphine)-1,4-hydroquinones, (2,5-bis(PiPr2)-3,6-difluoro-1,4-hydroquinone (1a), 2,5-bis(PiPr2)-1,4-hydroquinone (1b), (2,5-bis(PPh2)-3,6-difluoro-1,4-hydroquinone (1c), and 2,5-bis(PPh2)-1,4-hydroquinone (1d)) were investigated. Reactions of these ligands 1a–d with excess (∼2.5) of bis(cyclopentadienide)nickel, and in case of 1a, with bis(pentamethylcyclopentadienide)nickel, resulted in the formation of bimetallic nickel complexes 2a–d and 3a, where both [P,O] chelating pockets of the ligands were occupied by CpNi or Cp∗Ni moieties, respectively. Cyclic voltammetric (CV) scans on complexes 2a–d contained a common feature of two reversible/quasi-reversible waves and one irreversible redox event. Complex [2a][PF6] was isolated by the oxidation of 2a with ferrocenium hexafluorophosphate. Spectroscopic, structural, and synthetic studies were carried out in order to elucidate the nature of these redox processes. Our results suggest that the reversible and quasi-reversible redox events are ligand-based processes (hydroquinone/semiquinone/quinone), while the irreversible process was assigned as metal-based. These conclusions were supported by additional experimental data and by theoretical calculations. Investigations of chemical reactivity showed that cyclopentadienide ligands in complexes 2a–d can be displaced from the metal centers upon reactions with o-aminothiophenol. One of these derivatives, 4a, containing capping [N,S] o-aminothiophenolate ligands was isolated and fully characterized. A CV scan of complex 4a contained one reversible wave and an irreversible wave at higher potentials. The assignment is complicated by the proton transfer processes accompanying the electron transfer events. Complexes 1a, 2a–c, [2a][PF6] and 4a were characterized by single crystal X-ray diffraction experiments.

Bis-cyclometalated complexes of Pd(II) and Pd(IV) from iminophosphoranes: Synthesis, structure and reactivity

The mononuclear bis-orthopalladated complexes [Pd(CˆN){C6H4(PPh2NPh)-2}] [CˆN = (2-(pyridin-2-yl)phenyl) 3a, (2-((dimethylamino)methyl)phenyl) 3b, (S)-(2-(1-(dimethylamino)ethyl)phenyl) 3c, (quinolin-8-ylmethyl) 3d, (4-methoxy-2-((triphenyl-λ5-phosphanylidene)carbamoyl)phenyl) 3e] have been synthesized as single isomers by reaction of the corresponding chloride dimers [Pd(μ-Cl)(CˆN)]2 (1a–1e) with the lithium derivative [Li{C6H4(PPh2NPh)-2}] (2) in Et2O. Spectroscopic data show that the two palladated C atoms are in cis disposition, which is confirmed by the X-ray structure of 3a. Oxidation of 3a with PhI(OAc)2 affords the corresponding Pd(IV) derivative (OC-6-32)[Pd(OAc)2{C6H4(PPh2NPh)-2}{C6H4-(2′-NC5H4)-2}] 4a also as a single isomer. 4a undergoes reductive elimination through C–O coupling to give the dimer [Pd(μ-OAc){C6H4(PPh2NPh)-2}]25 and the ortho-acetoxylated phenylpyridine 6. The reactivity of 3b–3e towards oxidants is also discussed.

Electrochemical Oxidation of Acetaminophen and 4-(Piperazin-1-yl)phenols in the Presence of 4-Hydroxy-1-methyl-2(1H)-quinolone

A facile and one-pot electrochemical method for the synthesis of mono and disubstituted 1,4-benzoquinones generated from the electrochemical oxidation of 1-(4-(4-hydroxyphenyl)piperazin-1-yl)ethanone (1a), 4-(piperazin-1-yl)phenol (1b) and acetaminophen (8) in the presence of 4-hydroxy-1-methyl-2(1H)-quinolone (3) as nucleophile was reported. The results revealed that the electrochemically generated electrophiles derived from the oxidation of 1a, 1b and 8 participate in Michael-addition reactions with 3. In this work, we report the synthesis of mono and diquinolone substituted of 1,4-benzoquinone in good yields based on controlled potential condition at carbon electrode in a divided cell.

Cyclic Phosphinates by the Alkylation of a Thermally Unstable 1-Hydroxy-1,2- Dihydrophosphinine 1-Oxide and A 3-Hydroxy-3-Phosphabicyclo[3.1.0]Hexane 3-Oxide

1-alkoxy-1,2-dihydrophosphinine oxides 4 may be prepared by the reaction of 1-hydroxy-1,2-dihydrophosphinine 1-oxide 3 with alkyl halides. The best results were obtained in boiling acetone in the presence of K2CO3. The outcome of the alkylation of 3-hydroxy-6,6-dichloro-3-phosphabicyclo[3.1.0]hexane 3-oxide 5 was dependent on temperature. Butylation at 56 °C in acetone using K2CO3 afforded mainly the expected phosphinate 6, but an increase in the temperature led to opening of the cyclopropane ring, resulting in the formation of 1-butoxy-1,2-dihydrophosphinine oxide 4a as the major product.

Reactivity of the bridged-sulfide complex Pd2Cl2(μ-S)(μ-dmpm)2toward electrophiles

The dipalladium(I) complex Pd(2)Cl(2)(dmpm)(2) (1a) [dmpm = bis(dimethylphosphino)methane] is known to react with elemental sulfur (S(8)) to give the bridged-sulfide complex Pd(2)Cl(2)(μ-S)(dmpm)(2) (2a) but, in the presence of excess S(8), PdCl(2)[P,S-dmpm(S)] (4a) and dmpm(S)(2) are generated. Treatment of 1a with elemental selenium (Se(8)), however, gives only Pd(2)Cl(2)(μ-Se)(dmpm)(2) (3a). Complex 4a is best made by reaction of trans-PdCl(2)(PhCN)(2) with dmpm(S). Complex 2a reacts with MeI to yield initially Pd(2)I(2)(μ-S)(dmpm)(2) and MeCl, and then Pd(2)I(2)(μ-I)(2)(dmpm)(2) and Me(2)S, whereas alkylation of 2a with MeOTf generates the cationic, bridged-methanethiolato complex [Pd(2)Cl(2)(μ-SMe)(dmpm)(2)]OTf (5). Oxidation of 2a with m-CPBA forms a mixture of Pd(2)Cl(2)(μ-SO)(dmpm)(2) and Pd(2)Cl(2)(μ-SO(2))(dmpm)(2), whereas Pd(2)Br(2)(μ-S)(dmpm)(2) reacts selectively to give Pd(2)Br(2)(μ-SO)(dmpm)(2) (6b). Treatment of the Pd(2)X(2)(μ-S)(dmpm)(2) complexes with X(2) (X = halogen) removes the bridged-sulfide as S(8), with co-production of Pd(II)(dmpm)-halide species. X-ray structures of 3a, 5 and 6b are presented. Reactions of dmpm with S(8) and Se(8) are clarified. Differences in the chemistry of the dmpm systems with that of the corresponding dppm systems [dppm = bis(diphenylphosphino)methane] are discussed.

Synthesis and Biological Evaluation of Diastereomeric (E and Z) Sulfides, Sulfones, Sulfide-Sulfones, and Disulfones

The addition of p-chlorobenzenethiol to benzyl p-chlorophenylketone resulted in the formation of a mixture of diastereomers (E)- and (Z)-1-p-chlorophenyl-2-phenyl-1-p-chlorophenylthioethylene (1 and 2). These compounds, upon reaction with bromine in acetic acid, yielded a mixture of (E)- and (Z)-1-bromo-2-p-chlorophenyl-1-phenyl-2-p-chlorophenylthioethylenes (5a and 5b). Oxidation of 5a and 5b affords (E)- and (Z)-1-bromo-2-p-chlorophenyl-1-phenyl-2-p-chlorophenylsulfonylethylenes (6a and 6b), which upon reaction with the p-chlorobenzenethiol gave (E)- and (Z)-1-p-chlorophenyl-1-p-chlorophenylsulfonyl-2-phenyl-2-p-chlorophenylthioethylenes (7a and 7b). Oxidation of 7a and 7b yielded (E)- and (Z)-1,2-bis(p-chlorophenylsulfonyl)-2-phenyl-1-p-chlorophenylethylenes (8a and 8b). The final products, 8a and 8b, were also synthesized from a mixture of diastereomers, (E)- and (Z)-2-p-chlorophenyl-1-phenyl-1-p-chlorophenylthioethylenes (3 and 4), yielding the intermediates 9a and 9b, 10a and 10b, and 11a and 11b. The configurations of these compounds were established by elemental analysis, IR, 1H NMR, and mass spectra, and by their preparation from the corresponding phenylketones and p-chlorophenylphenylacetylene. All these new compounds exhibited pronounced in vitro antibacterial and antifungal activities. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. GRAPHICAL ABSTRACT

ChemInform Abstract: Oxidation of Bis(tert-butylthio) Selenide at Low Temperatures: Search for a Bis(alkylthio) Selenoxide.

Oxidation of bis(tert-buthylthio) selenide, t-BuSSeSBu-t (1a), by peracetic acid at −40°C leads to a monooxidation product (1a-O) whose 1 H (two singlets) and 13 C NMR spectra (four resonances) show that the two tert-butyl groups in 1a-O are magnetically nonequivalent. Oxidation of 1a by peracid is examinated

ChemInform Abstract: 1,2-Disiladioxetanes: Structure, Rearrangement, and Reactivity.

The low-temperature reaction of (E)-1,2-dimesityl-1,2-di-tert-butyldisilene (1a) with dioxygen gives (E)-1,2-dimesityl-1,2-di-tert-butyldisiladioxetane (2a), the structure of which has been established by X-ray crystallographic analysis. This result establishes that both oxidation of 1a and rearrangement of 2a to 1,3-cyclodisiloxane 4a take place with retention of configuration at silicon. Disiladioxetane 2a forms monoclinic crystals, space group C2/c. extra electron density found above and below the Si-Si bond was shown by 1 H and solid-state 29 Si NMR to be due to 4a, arising from rearrangement of 2a in the solid. X-ray crystal structures were determined for crystals that were 5.6%, 15.2%, and 20.3% rearranged