Expected Substitution Products Research Articles

Synthesis and Unusual Reactivity of Acyl-Substituted 1,4-Disilacyclohexa-2,5-dienes.

In continuation of our recent studies on group 14 rings with exocyclic silicon-carbon double bonds, we report here on the synthesis and reactivity of previously unknown acyl-substituted 1,4-disilacyclohexa-2,5-dienes. 1,1,4,4-Tetrakistrimethylsilyl-1,4-disilacyclohexa-2,5-diene 1 cleanly afforded the silyl anion 1-K after addition of 1 equiv of KO t Bu. 1-K subsequently could be reacted with various electrophiles to the expected substitution products including compounds 4 and 5. When photolyzed with λ > 300 nm radiation, 4 and 5 undergo Brook-type 1,3-Si → O migration reactions to generate the corresponding 1,4-disilacyclohexadienes with exocyclic Si=C bonds as the primary products. These metastable silenes only could be characterized in form of appropriate quenching products. The reaction of compound 4 with KO t Bu followed by the addition of 1 equiv of PhMe2SiCl surprisingly gave the silylated 1,4-disilanorbornadiene cages 8 and 9 instead of the expected exocyclic silene. The responsible sila-Peterson-type mechanism could be elucidated by density functional theory calculations at the conductor-like polarizable continuum model (THF) B3LYP-GD3/6-31 + G(d) level and by the isolation and characterization of unstable intermediate products after proper derivatization.

(2R,3R)-3-[(1R)-1-{[tert-Butyl(dimethyl)silyl]oxy}ethyl]-4-oxoazetidin-2-yl Acetate in Zinc- and Samarium-Promoted Substitution Reactions with Methyl 2-Bromopropanoate and Methyl (2-Bromomethyl)prop-2-enoate. Unusual Cleavage of the N1‒C4 Bond in Azetidin-2-one Derivative with Migration of Methoxycarbonyl Group in Synthetic Approaches to Carbapenems and Their Analogs

The use of zinc in Barbier-type reactions of (2R,3R)-3-[(1R)-1-{[tert-butyl(dimethyl)silyl]oxy}-ethyl]-4-oxoazetidin-2-yl acetates with halogen derivatives led to the formation of expected substitution products. The reaction of the title compound with a reagent prepared from samarium powder, a catalytic amount of iodine, and methyl 2-bromopropanoate in THF gave an anomalous substitution product, methyl 2-{(2S,3S)-3-[(1R)-1-{[tert-butyl(dimethyl)silyl]oxy}ethyl]-4-oxoazetidin-2-yl}-2(R,S)-methyl-3-oxopentanoate. Alkylation of the latter with methyl bromoacetate afforded methyl 2-{(2S,3S)-3-[(1R)-1-{[tert-butyl(dimethyl) silyl]oxy}ethyl]-1-(2-methoxy-2-oxoethyl)-4-oxoazetidin-2-yl}-2(RS)-methyl-3-oxopentanoate which underwent fragmentation through cleavage of the N1–C4 bond under the action of sodium bis(trimethylsilyl)-amide in THF at–78°C. The resulting acyclic amide, dimethyl {(2R,S,3Z)-2-[(1R)-1-{[tert-butyl(dimethyl)-silyl]oxy}ethyl)]-4-methyl-5-oxohept-3-enoylamino}malonate, was smoothly converted to new functionalized N-substituted pyrrolidinones via intramolecular Michael type cyclization in methylene chloride in the presence of NEt3–DMAP–Boc2O.

Alternative syntheses and reactivity of platinum(II) terpyridyl acetonitrile complexes

New direct syntheses of [Pt(trpy)(NCCH 3)](CF 3SO 3) 2 2 (where trpy = 2,2′:6′,2′′-terpyridine) and [Pt( tBu 3-trpy)(NCCH 3)](CF 3SO 3) 2 3 (where tBu 3-trpy = 4,4′,4″-tri- tert-butyl-2,2′:6′,2″-terpyridine) via the displacement of acetonitrile from [Pt(NCCH 3) 4](CF 3SO 3) 2 have been developed. The synthetic utility of 2 was investigated in reactions with triphenylphosphine (PPh 3), 2,6-dimethylphenyl isocyanide (CN-Xyl), 2,5-dimethyl-2,5-diisocyanohexane (TM4), and tert-butyl isocyanide (CN- tBu). Whereas the expected substitution products were observed for reactions with PPh 3, CN-Xyl, and CN- tBu, dealkylation of TM4 occurred to afford [Pt(trpy)(CN)](CF 3SO 3) 6. The structures of [Pt(trpy)L] 2+ dications show little intermolecular interactions in the solid state, with the exception of the tBu 3-trpy complex 3 which exists as head-to-tail dimers with a Pt–Pt distance of 3.29 Å. The cyano product 6 was found to stack in infinite chains of cations with a Pt–Pt distance of 3.45 Å.

S EAr–S NAr couplings of indolizines and related pyrrole derivatives with superelectrophilic nitrobenzoxadiazoles

The nucleophilic aromatic substitutions of 7-chloro-4,6-dinitrobenzofurazan (DNBZ-Cl) and 7-chloro-4,6-dinitrobenzofuroxan (DNBF-Cl) with a series of differently substituted indolizines ( 5a– f) and a series of dihyropyrroloisoquinolines ( 11a– f) have been investigated. In accord with previous reports emphasizing the superelectrophilic character of these compounds in σ-complexation processes, DNBZ-Cl and DNBF-Cl react very readily and quantitatively with the weak carbon nucleophiles 5a– f and 11a– f at room temperature in acetonitrile. In the case of DNBZ-Cl, the resulting products ( 7Z, a– f and 12Z, a– f) are those expected from the displacement of the chlorine atom through a S EAr–S NAr mechanism. A significant result is that these compounds, despite the lack of coplanarity of the two rings, are characterized by an intense intramolecular charge transfer between the donor pyrrole-type moiety and the electron-deficient acceptor DNBZ moiety. Contrasting with this behaviour, the DNBF-Cl reactions show a totally different pattern, proceeding with loss of the N-oxide functionality and expansion of the pyrrole moiety to afford stable zwitterionic spiro adducts ( 8F, a– f and 13F, a– f) of a so far unknown type. Rapid NMR recordings have revealed that the formation of these adducts occurs after initial formation of the expected substitution products 7F, a– f and 12F, a– f. A mechanism accounting for the overall rearrangement leading to the spirobenzofurazan adducts is suggested. It is based on an initial nucleophilic attack of the oxygen atom of the N-oxide functionality at the electron-deficient and strongly olefinic C–C coupling bond generated by the aforementioned intramolecular charge transfer. This results in the formation of an unstable five-membered isoxazole ring whose decomposition goes along with loss of the N-oxide functionality and enlargement of the pyrrole moiety into a pyridine one. Also discussed are the factors accounting for the high thermodynamic stability of the spiro adducts, and their relevance to the stability of previously reported spiro adducts.

Organouranium Complexes with Phosphinine-Based SPS Pincer Ligands. Variations with the Substituent at the Phosphorus Atom

Reaction of [K(Et2O)][SPSMe] with [U(Cp*)(BH4)3] or [U(COT)(BH4)2(THF)] in THF gave the expected substitution products [U(Cp*)(BH4)2(SPSMe)] (1) and [U(COT)(BH4)(SPSMe)] (2), respectively. Protonolysis of 2 with [NEt3H][BPh4] afforded the cationic complex [U(COT)(SPSMe)(NEt3)][BPh4] (3), which was transformed into [U(COT)(SPSMe)(L)][BPh4] [L = OPPh3 (4) or HMPA (5)]. Changing [K(Et2O)][SPSMe] with [Na][SPSOMe] in its reaction with [U(COT)(BH4)2(THF)] afforded a mixture of complexes, among which [U(COT)(BH4)(SPSH)] (6) was deposited as red crystals of a THF solvate. Complex 6 was isolated in 79% yield from the reaction of [U(COT)(BH4)2(THF)] and SPS in the presence of a catalytic amount of NaBH4; the key intermediate of the reaction is [Na(THF)x][SPSH·BH3], formed by addition of NaBH4 to SPS, which reacts with [U(COT)(BH4)2(THF)] to give 6 and NaBH4. The X-ray crystal structures of 1·4.5C6H12, 2·THF, 5·Et2O, and 6·1.5THF indicate that the central moiety of the SPS ligand can be considered as a classical phosphine, the anionic charge being stabilized by delocalization over the five carbon atoms of the phosphahexadienyl anion and negative hyperconjugation into the two Ph2PS pendant arms. The X-ray crystal structures of [{U(COT)(S2PPh2)(μ-OMe)}2] and [{U(COT)}4{U(THF)3}2(μ3-S)8], which resulted from decomposition of the SPS ligand, are also presented.

Preparation, Structural Characterization, and Reactivities of (Digermanyl)lithium. Its Application to the Synthesis of Bis(1,1-diphenyl-2,2,2-trimethyldigermanyl)platinum(II)

Abstract (Pentamethyldigermanyl)lithium (Me3GeGeMe2Li, 1a) and (1,1-diphenyl-2,2,2-trimethyldigermanyl)lithium (Me3GeGePh2Li, 1b) were prepared and characterized by spectroscopic methods. The structure of (digermanyl)lithium 1b was established by X-ray diffraction. The reaction of 1b with cis-PtCl2(PMe2Ph)2 gave the expected substitution product, trans-Pt(Me3GePh2Ge)2(PMe2Ph)2.

A Benzyloxy Group Migration under Mitsunobu Reaction Conditions.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A benzyloxy group migration under Mitsunobu reaction conditions

When compounds 3a and 3b were subjected to a Mitsunobu reaction with benzoylthymine, the expected substitution products were formed together with the regioisomers corresponding to benzyloxy group migrations.

Synthesis of cobalt-containing cyclophanes, and the formation of an unprecedented seven-membered cyclic diyneElectronic supplementary information (ESI) available: crystallographic data for complexes 8 and 11. See http://www.rsc.org/suppdata/nj/b3/b310515f/

The acid-catalysed Nicholas reaction of the bis-propargyl complex [{Co2(CO)6(μ-η2-HOMe2CCC–)}2] 1 in the presence of a variety of nucleophiles leads in each case to [{Co2(CO)6}2{cyclo-μ-η2:μ-η2-C(CH2)CH2CMe2CC–CC}], a complex which contains an unprecedented seven-membered macrocyclic diyne ligand. The reactivity of 1 is compared to that of [{Co2(CO)6}2{μ-η2:μ-η2-1,4-C6H4(CCCMe2OH)2}] which does not cyclise on treatment with nucleophiles but instead gives the expected substitution products.

The Reaction of Triptycene Haloquinones with Alkoxides. An Unusual Route to Pentiptycene Quinones.

AbstractFor Abstract see ChemInform Abstract in Full Text.

The reaction of triptycene haloquinones with alkoxides. An unusual route to pentiptycene quinones

Triptycene haloquinones 3 react with sodium alkoxides in refluxing alcohol to afford, besides the expected substitution products, pentiptycene quinone 4 . This approach to 4 is compared with a Diels–Alder strategy to the same compound.

Sigma-complex formation and oxidative nucleophilic aromatic substitution in 4-nitro-2,1,3-benzoxadiazoles.

The feasibility of carrying out nucleophilic displacement of hydrogen from highly electron-deficient heteroaromatics has been addressed through a detailed investigation of the interaction of a series of nitrobenzofuroxans 3a-i and two related heterocycles 5 and 6, with the 2-nitropropenide anion. Although this series corresponds to a large modulation in the electrophilic properties of the six-membered ring, all reactions first lead to the quantitative formation of the sigma-adducts C-3a-i, C-5 and C-6 arising from covalent addition of the nucleophile to the C-7 carbon. With the exception of the 4-aza substituted member C-5, all the adducts have been isolated as pure and very stable alkali salts. Measurements of the oxidation potentials by cyclic voltammetry reveal that the ease of subsequent hydrogen substitution at carbon-7 strongly decreases with increasing electron deficient character of the six-membered ring. The measured E0 values are in the range 0.5-0.6 V (vs. SCE) for the 4-nitro-benzofuroxan and -benzofurazan adducts (C-3e, C-3i) but they go up to 1.20-1.33 V for the 4,6-dinitro- and 4-nitro-6-trifluoromethanesulfonylbenzofuroxan adducts (C-3a,d) in acetonitrile. Consistently with these E0 values, only very powerful oxidants such as the Ce4+/Ce3+ or the MnO4-/Mn2+ couples can successfully oxidize the adducts leading to the expected substitution products in moderate to good yields (35-72%). Interestingly, the rearomatization of the 4-nitro substituted benzofuroxan adducts proceeds with a partial Boulton-Katritzky rearrangement of the resulting products. Another noteworthy result is that the 4-nitrobenzofuroxan and 4-nitrobenzofurazan molecules suffer competitive addition of the (CH3)2C-NO2- anion to the 5- and 7- positions under some experimental conditions. This represents the first well-defined example of isomeric addition of a carbon nucleophile to these heterocycles.

Hydrazino Derivatives of Gallanes and Indanes − Synthesis and Structures

The reaction of Me2GaCl with tBuHN−NH2 proceeds with ligand exchange at the gallium atom leading to MeCl2Ga·H2N−NHtBu (1). On the other hand, only one methyl group of the trimethylgallium molecule reacts in refluxing toluene with anhydrous hydrazine in a 4:3 ratio to produce the bicyclic dimethylgallium hydrazide 3. N-Lithio-N-trimethylsilyl-N′-2-naphthylhydrazine reacts with dimethylgallium chloride, not only by introducing a gallium atom into the hydrazine unit, but also by inducing CH activation at the 1-position of the naphthyl group with methane evolution. The main product isolated is the 2,3-dihydro-1H-naphtho[1,2-d][1,2,3]diazagallol 4 which proved to be dimeric. A 1:1 GaMe3 adduct of Li(Me3Si)N−NHtBu (5) is the unexpected compound in the reaction of Me2GaCl with Li(Me3Si)N−NHtBu. The expected substitution product Me2Ga(Me3Si)N−NHtBu is not formed. Compound 5 is a dimer in the solid state. The products obtained from reactions of Li(Me3Si)N−NHtBu with Me2InCl depend on the solvent. With hexane as a solvent the dimeric trimethylindium adduct of Li(Me3Si)N−NHtBu (7), is produced as the main species. In diethyl ether the cage compound 8 is isolated which can be regarded as an (Me3SiN=InMe)2 adduct with [Li(Me3Si)N−NHtBu]2. Moreover, the reaction of Me2InCl in diethyl ether with the bulky lithium hydrazide Li[Me3SiN−N(SiMe3)2] leads not to the substitution product, but to the dimeric adduct 9 of a diindoxane, Me2In−O−InMe2 with Li(Me3Si)N−N(SiMe3)2. The formation of this product indicates that ether cleavage or hydrolysis (during crystallization) has occurred.

Detection and kinetic characterization of SNV intermediates. Reactions of thiomethoxybenzylidene Meldrum's acid with thiolate ions, alkoxide ions, OH-, and water in aqueous DMSO

The reaction of thiomethoxybenzylidene Meldrum's acid (5-SMe) with thiolate and alkoxide ion nucleophiles is shown to proceed by the two-step addition-elimination SNV mechanism in which the tetrahedral intermediate accumulates to detectable levels. For the reactions with thiolate ions, rate constants for nucleophilic addition (k1RX), its reverse (k-1RX), and for conversion of the intermediate to products (k2RX) were determined. For the reactions with alkoxide ions, only k1RXand k-1RXcould be obtained; the intermediate in these reactions did not yield the expected substitution products, and hence no k2RXvalues could be determined. The reactions with OH-and water are believed to follow the same mechanism, but the respective intermediates remain at steady-state levels, and only k1OHand k1H²Ofor nucleophilic attack on 5-SMe were measurable. New insights regarding structure-reactivity behavior in SNV reactions are gained from comparisons of rate and equilibrium constants in the reactions of 5-SMe with the corresponding parameters in the reactions of methoxybenzylidene Meldrum's acid (5-OMe) and benzylidene Meldrum's acid (5-H). In particular, the relative importance of steric and pi-donor effects of the MeS vs. MeO group in 5-SMe and 5-OMe, respectively, and their role in affecting the intrinsic rate constants for nucleophilic addition, has been clarified by these comparisons. Our results also add support to a previous suggestion that soft-soft type interactions tend to increase intrinsic rate constants for thiolate ion addition to vinylic substrates, especially 5-SMe with the soft MeS group.Key words: nucleophilic vinylic substitution, intrinsic rate constants, transition state imbalances, steric/pi-donor/anomeric effects.

Detection and kinetic characterization of S<sub>N</sub>V intermediates. Reactions of thiomethoxybenzylidene Meldrum's acid with thiolate ions, alkoxide ions, OH<sup>-</sup>, and water in aqueous DMSO

The reaction of thiomethoxybenzylidene Meldrum's acid (5-SMe) with thiolate and alkoxide ion nucleophiles is shown to proceed by the two-step addition-elimination SNV mechanism in which the tetrahedral intermediate accumulates to detectable levels. For the reactions with thiolate ions, rate constants for nucleophilic addition (k1RX), its reverse (k-1RX), and for conversion of the intermediate to products (k2RX) were determined. For the reactions with alkoxide ions, only k1RX and k-1RX could be obtained; the intermediate in these reactions did not yield the expected substitution products, and hence no k2RX values could be determined. The reactions with OH- and water are believed to follow the same mechanism, but the respective intermediates remain at steady-state levels, and only k1OH and k1H²O for nucleophilic attack on 5-SMe were measurable. New insights regarding structure-reactivity behavior in SNV reactions are gained from comparisons of rate and equilibrium constants in the reactions of 5-SMe with the corresponding parameters in the reactions of methoxybenzylidene Meldrum's acid (5-OMe) and benzylidene Meldrum's acid (5-H). In particular, the relative importance of steric and pi-donor effects of the MeS vs. MeO group in 5-SMe and 5-OMe, respectively, and their role in affecting the intrinsic rate constants for nucleophilic addition, has been clarified by these comparisons. Our results also add support to a previous suggestion that soft-soft type interactions tend to increase intrinsic rate constants for thiolate ion addition to vinylic substrates, especially 5-SMe with the soft MeS group.Key words: nucleophilic vinylic substitution, intrinsic rate constants, transition state imbalances, steric/pi-donor/anomeric effects.

Carboxylate Bridged Octaphenyltetra-antimony (V) ‘Cage’ Compounds; [(SbPh2)4(μ-O)4(μ-OH)2(μ-O2CR)2· HO2CR], where R = Me or t-Bu and the Crystal Structure of [(SbPh2)4(μ-O)4(μ-OH) (μ-OEt)(μ-O2CMe)2

Reactions of [SbPh2BrO]2 with carboxylates did not give [SbPh2(O2CR[2, the expected substitution products, which are highly sensitive to hydrolysis by traces of moisture, and cage compounds containing an Sb4O6 unit were obtained instead. With silver acetate and sodium trimethylacetate the products were [(SbPh2)4(μ-O)4(μ-OH)2(μ-O2CR)2]·HO2CR, R = Me 1 and R = t-Bu 2, respectively. An unusual compound, [(SbPh2)4(μ-O)4(μ-OH)(μ-OEt(μ-O2CMe)2] 3, in which one of the bridging hydroxo groups in 1 is replaced by an ethoxo group, was also isolated and its crystal structure determined.

The direct preparation of protected hydrazines from alcohols via Mitsunobu chemistry

A general method for converting primary and secondary alcohols to protected hydrazines using the Mitsunobu reaction is reported. The reaction of α-hydroxy esters affords dihydrohydrazino esters rather than the expected substitution product.

Verbindungen mit dem 5,6-Benzo-l,3,2-diazaphosphorinan-4-on-Ringsystem: Synthese von 2-Chlor-, 2-N,N-dimethylamino-und 2-Bis-(2-chlorethyl)amino- substituierten Derivaten mit drei-und vierfach koordiniertem Phosphor / Compounds Involving the 5,6-Benzo-l,3,2-diazaphosphorinane-4-one Ring System: Synthesis of 2-Chloro-, 2-N,N-dimethylamino-and 2-Bis-(2-chloroethyl)amino- Substituted Derivatives with Three-and Four-Coordinated Phosphorus

The reaction of methylisatoic anhydride with 2-(aminomethyl)pyridine, 3-(aminomethyl)- pyridine, 3-dimethylamino-1-propylamine, 3-diethylamino-1-propylamine and 3-dibutylamino- 1-propylamine furnished the N-substituted N'-methylanthranilic amides 1-5. In the reaction of 1-5 with phosphorus trichloride the 3-substituted 5,6-benzo-1-m ethyl-1,3,2-diazaphosphorinane- 4-one derivatives 6 to 10 were obtained. The possibility of intramolecular donoracceptor interaction between the nitrogen atom of the R2N group and the λ3P atom is suggested on the basis of 1H NMR studies. The reaction of 9 with dimethylamino-trimethylsilane furnished the 2-dimethylamino-substituted product 11. In the reaction of 6, 7 and 10 with bis-(2-chloroethyl)amine hydrochloride/triethylamine the expected substitution products 12 to 14 were obtained. 5,6-Benzo-2-[bis-(2-chloroethyl)amino]-1-methyl-3-(3-picolyl)-1,3,2-diazaphosphorinan- 4-one 13 reacted with (COD)PtCl2 to give the czs-dichloro-platinum(II) complex 15. The characterisation of 1-15 is based on the 1H-, 13C-, and 31P-NMR spectra, mass spectra and X-ray structure determinations of the precursor compounds 1 and 3

Umsetzungen von 0,3-Dialkyl-1,3-diaza-2-chloro-5,6-benzo-1,3,2-phosphorinan-4-onen; Darstellung von P(III)-Derivaten / Reactions of 1,3-Dialkyl-1,3-diaza-2-chloro-5,6-benzo-1,3,2-phosphorinan-4-ones; Preparation of P(III) Derivatives

The reaction of 1,3-dimethyl-1,3-diaza-2-chloro-5,6-benzo-1,3,2-phosphorinan-4-one 1 with N-trimethylsilylacetamide 2 and 2-methylpiperidine hydrochloride furnished the P-substituted derivatives 3 and 4. The reaction of 1 with trimethylbromo- and trimethyliodosilane yielded the 2-bromo- and 2-iodo- substituted compounds 5 and 6. 1-Methyl-3-(2-chloroethyl)-1,3-diaza-2-chloro-5,6-benzo-1,3,2-phosphorinan-4-one 8 was prepared in the reaction of N-methyl-N'-(2-chloroethyl)-anthranilamide 7 with phosphorus trichloride. The reaction of 8 with N-trifluoromethyl-3-nitrophenylamine 9 or with sodium fluoride led to the 2-fluorosubstituted product 11. From the unusual reaction of 8 with 9 in the presence of triethylamine N-difluoromethylene-3-nitrophenylimine 10 and the intermediate product, triethylamine hydrofluoride, were isolated. A mechanism of formation of 11 is proposed. The reaction of 8 with N-trimethylsilylacetamide 2 and bis-2-chloroethylamine hydrochloride furnished the expected substitution products 14 and 15, involving the 5,6-benzo-1,3,2-phosphorinan-4-one ring system. The characterization of 3-6, 8, 11, 14 and 15 rests, especially, on their 1H-, 13Cand 31P-NMR spectra, and their mass spectra.

Cyclization Reactions in Azole Chemistry: The Reaction of Some Azoles With o-Fluoroacetophenone, o-Fluorobenzaldehyde and o-Fluorobenzophenone

The reactions of some azoles with o-fluoro-acetophenone , -benzaldehyde and -benzophenone in dimethyl sulfoxide solution in the presence of anhydrous potassium carbonate have been investigated. In addition to the expected substitution products, cyclization reactions frequently occurred to give carbinols in the case of the reactions of o-fluoro-acetophenone and -benzophenone, and cyclic ketones in the case of the reactions with o-fluorobenzaldehyde . Fluoren-9-ol and related carbinols containing heteroaromatic nuclie are readily converted in dimethyl sulfoxide solution into the corresponding ketones by treatment with anhydrous potassium carbonate. When treated with ethanolic alkali, 2′-(benzimidazol-1′-yl) acetophenone undergoes a remarkable transformation to give 1-(2𔈊-aminophenyl)quinolin-4(1H)-one.