Acid-induced Ring Opening Research Articles

Multifunctional switching properties of "wire-like" dinuclear ruthenium bis-alkynyl spiropyran complexes.

Multifunctional switches are crucial to the development of smart molecular materials and molecular-electronic applications. Here, we describe the synthesis, structure, and characterization of several spiropyrans functionalized with alkynyl-[Ru(dppe)2] moieties. Through electrochemical and spectroelectrochemical studies, we demonstrate access to several stable redox states, in addition to states accessed via acidochromism and photoisomerisation. Initial protonation was found to occur at the alkynyl functionality followed by acid-induced ring-opening of the spiropyran ligand to form the protonated merocyanine. The protonated merocyanine can be switched from the Z- to E-isomer by using ultraviolet light. The spiropyran was also shown to be an effective insulator for electronic communication across the molecular backbone.

Proton-Stabilized Photochemically Reversible E/ Z Isomerization of Spiropyrans.

Spiropyrans undergo Cspiro–O bond breaking to their ring-open protonated E-merocyanine form upon protonation and irradiation via an intermediate protonated Z-merocyanine isomer. We show that the extent of acid-induced ring opening is controlled by matching both the concentration and strength of the acid used and with strong acids full ring opening to the Z-merocyanine isomer occurs spontaneously allowing its characterization by 1H NMR spectroscopy as well as UV/vis spectroscopy, and reversible switching between Z/E-isomerization by irradiation with UV and visible light. Under sufficiently acidic conditions, both E- and Z-isomers are thermally stable. Judicious choice of acid such that its pKa lies between that of the E- and Z-merocyanine forms enables thermally stable switching between spiropyran and E-merocyanine forms and hence pH gating between thermally irreversible and reversible photochromic switching.

ChemInform Abstract: Acid-Induced Ring Opening of α-(Bis(methylthio)methylene)alkyl Cyclopropyl Ketones: A Novel Route to Substituted Cyclopentanones Through Carbocationic Cyclizations.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Palladium-, Platin- und Dieisenkomplexe mit Isocyanacetat: Ringschluß, säureinduzierte Ringöffnung, Diprotonierung

Palladium, Platinum, and Diiron Complexes with Isocyanoacetate: Ring Closure, Acid-Induced Ring Opening, Diprotonation Substitution by isocyanoacetate (CNCH2CO2−) of one chloro ligand in trans-[MCl2(PPh3)2] (M = Pd, Pt) results in the Δ2-oxazolin-5-on-2-ato complexes 4a, b, i.e. immediate cyclization occurs in contact with these metal(II) species. In contrast, the open-chain form of the functional isocyanide is retained in [K(18-crown-6][Fe2Cp2(CNCH2CO2)(CO)3] (16) in which it occupies a terminal position. Protonation (alkylation) of the platinum complex 4b proceeds with ring cleavage and formation of isocyano acetic acid 11 (ethyl isocyanoacetate 12) stabilized by metal ion coordination. Protonation of 16 requires two equivalents of acid to yield the aminocarbyne-bridged complex [{μ-C=N(H)CH2CO2H}Fe2Cp2(CO)3](BF4) (17) as the only isolable product. Here isocyanoacetate displays a third kind of reactivity pattern in addition to that at PdII/PtII and that at Cr0/W0 where the primary species [M(CO)5CNCH2CO2]− and [M(CO)5CNCH2CO2H] proved to be the most stable. All of the proposed structures are substantiated by analytical and the usual spectroscopic (IR, NMR{1H, 13C, 31P}, FAB-MS) data, that of 4b also by an X-ray structure determination which reveals a practically perpendicular arrangement of the coordination and the ring plane, and a long C2-O bond as the predetermined breaking point of the heterocycle.

Diels-Alder reactions using 4,7-dioxygenated indanones as dienophiles for regioselective construction of oxygenated 2,3-dihydrobenz[f]indenone skeleton.

Regioselective construction of 4,8,9-trioxygenated 2,3-dihydrobenz[f]indenones, key intermediates for the synthesis of kinamycin antibiotics, was achieved via Diels-Alder reactions (DAR) using 4,7-dioxygenated indanone-type compounds as dienophiles. Reaction of indanetrione with 1-methoxybutadiene gave a 1 : 1 mixture of undesired 4,5,9-trioxygenated 2,3-dihydrobenz[f]indenone and [4.4.3]propellane. The addition of Lewis acid did not affect the product ratio, whereas the use of the 6-bromoindanetrione exclusively afforded the latter propellane. On the other hand, DAR of benzyne derived from bromoindan and furan gave 5,8-epoxy-2,3-dihydrobenz[f]indene, which was subjected to acid-induced ring opening to give 2,3-dihydrobenz[f]indenone with undesired 4,5,9-trioxy functions.

Synthesis of Bicyclic Tertiary α-Amino Acids

Novel bicyclic alpha-amino acids, exo and endo-1-azabicyclo[2.2.1]heptane-2-carboxylic acid, 1-azabicyclo[2.2.1]heptane-7-carboxylic acid, and 1-azabicyclo[3.2.2]nonane-2-carboxylic acid have been readily synthesized for the generation of neuronal nicotinic receptor ligands. Alkylation of glycine-derived Schiff bases or nitroacetates with cyclic ether electrophiles, followed by acid-induced ring opening and cyclization in NH4OH, allowed for the preparation of substantial quantities of the three tertiary bicyclic alpha-amino acids.

Domino Carbocationic Cyclization of Functionalized Cyclopropyl Ketones: Facile One‐Pot Access to Peri‐ and Angularly Fused Polycyclic Aromatic and Heteroaromatic Frameworks.

Conjugate adducts obtained by base-induced 1,4-addition-elimination of various aryl/heteroaryl acetonitriles with 1-(2-arylcyclopropyl)-3,3-(bismethylthio)-2-propen-1-ones have been shown to undergo facile acid-induced domino carbocationic rearrangement yielding a variety of substituted tricyclic aromatic and heteroaromatic frameworks in high yields in a one-pot operation. The methodology provides efficient, high-yield routes for synthesis of novel substituted dihydrophenalenes, dihydrobenzo[d,e]anthracene, cyclopenta[a]naphthalene, and fused heteroaromatics such as substituted 4,5-dihydrobenzo[c,d]indole, dihydronaphtho[1,8-b,c]thiophene, dihydroindeno[5,4-b]- and -[4,5-b]-thiophenes, cyclopenta[a]carbazole, and dihydrocyclopenta[e]indazol-3-one derivatives. The probable mechanism of this interesting domino process appears to involve stepwise or concomitant acid-induced ring opening and intramolecular cyclocondensation of cyclopropyl ketones to give benzo-fused arene (or heteroarene) intermediates bearing a reactive benzylic carbocation that is captured intramolecularly either by a preexisting aromatic (or heteroaromatic) ring or by a newly formed benzene ring to give either peri-fused or angularly fused products, respectively. Thus, the overall domino process entails formation of two C-C bonds, a substituted benzene ring along with a peri-fused cyclohexane or angularly fused cyclopentane ring in a single operation.

Domino carbocationic cyclization of functionalized cyclopropyl ketones: facile one-pot access to peri- and angularly fused polycyclic aromatic and heteroaromatic frameworks.

Conjugate adducts obtained by base-induced 1,4-addition-elimination of various aryl/heteroaryl acetonitriles with 1-(2-arylcyclopropyl)-3,3-(bismethylthio)-2-propen-1-ones have been shown to undergo facile acid-induced domino carbocationic rearrangement yielding a variety of substituted tricyclic aromatic and heteroaromatic frameworks in high yields in a one-pot operation. The methodology provides efficient, high-yield routes for synthesis of novel substituted dihydrophenalenes, dihydrobenzo[d,e]anthracene, cyclopenta[a]naphthalene, and fused heteroaromatics such as substituted 4,5-dihydrobenzo[c,d]indole, dihydronaphtho[1,8-b,c]thiophene, dihydroindeno[5,4-b]- and -[4,5-b]-thiophenes, cyclopenta[a]carbazole, and dihydrocyclopenta[e]indazol-3-one derivatives. The probable mechanism of this interesting domino process appears to involve stepwise or concomitant acid-induced ring opening and intramolecular cyclocondensation of cyclopropyl ketones to give benzo-fused arene (or heteroarene) intermediates bearing a reactive benzylic carbocation that is captured intramolecularly either by a preexisting aromatic (or heteroaromatic) ring or by a newly formed benzene ring to give either peri-fused or angularly fused products, respectively. Thus, the overall domino process entails formation of two C-C bonds, a substituted benzene ring along with a peri-fused cyclohexane or angularly fused cyclopentane ring in a single operation.

Chiral ions in the gas phase. 5. Acid-induced methanolysis of optically active styrene oxide

The acid induced ring opening of (R)-(+) styrene oxide ( 1R) or (S)-(−) styrene oxide ( 1S) is investigated in the gas phase, at a temperature of 25 °C and in the presence of a labeled nucleophile (CH 3 18OH, CD 3OH, or H 2 18O). Various acid catalysts are generated in situ by γ radiolysis of the bulk gas (720 Torr of CH 4 or CH 3F). The mechanisms of the ring-opening reaction are assessed by modulating the composition of the gaseous mixture. Two reaction pathways are operative in the gas phase, both proceeding with the same regio- (100% at C α) and stereochemistry (55–67% inversion of the C α configuration). In the CH 3F/H 2 18O systems, a slow reaction takes place within a persistent proton-bound complex between the epoxide and the CH 3 18OH 2 + ion, formed by (CH 3) 2F +-methylation of H 2 18O (the intracomplex pathway). When methanol is present in the gaseous mixtures, the intracomplex process is superseded by a faster extracomplex reaction, involving the attack of an external methanol molecule on the O-protonated epoxide. The present results are discussed in the light of related gas-phase and solution data.

Highly Enantioselective Intermolecular Cu(I)-Catalyzed Cyclopropanation of Cyclic Enol Ethers. Asymmetric Total Synthesis of (+)-Quebrachamine.

A set of cyclic enol ethers derived from 2,3-dihydrofuran 35 and 3,4-dihydropyran 8 with a varying substitution pattern at the olefinic system were synthesized. Evans's ligand 5 with Cu(I)OTf was found to be an effective catalyst in the cyclopropanation reaction between cyclic enol ethers 14, 19, 28-31, and 33 and ethyl diazoacetate 6 to give diastereoselectivities up to exo/endo = 95:5 and enantioselectivities higher than 95% in nearly all cases. Because of the selective building of a quarternary carbon center and good yields in the formation of bicyclic structures 34c-h, the reaction was used as a key step in the asymmetric synthesis of (+)-quebrachamine 7, an indole alkaloid of the Aspidosperma family. After acid-induced ring opening of bicyclic compound 34f to lactone 40 followed by LiAlH(4) reduction to the masked aldehyde 41, a reaction with tryptamine gave intermediate 42. This alcohol was efficiently converted into the indole alkaloid (+)-quebrachamine 7 in an overall yield of 37% starting from the chiral synthon 34f. Moreover it revealed the absolute configuration of the quarternary center of the cyclopropanation product 34f to be S.

Molecular orbital calculations for acid induced ring opening reaction of spiropyran

It was found that the acid induced ring opening reaction of spiropyran proceeded in the dark to give the cis form which was further isomerized to the trans form by UV irradiation. The mechanisms of these reactions were well explained by molecular orbital calculations. The structure of the transition state of the acid induced ring opening reaction was optimized by MOPAC with PM3. The structure revealed the direction of the ring opening of spiropyran. Subsequent geometry optimizations gave a protonated open cis form as a transient of this dark reaction.

Tandem Dipolar Cycloaddition-Mannich Cyclization as an Approach to Tricyclic Nitrogen Heterocycles.

A series of 2-diazo-N-[2-(3,4-dimethoxyphenyl)ethyl]-N-hept-6-enoylmalonamides were prepared and treated with a catalytic amount of rhodium(II) perfluorobutyrate. The resultant carbenoids undergo facile cyclization onto the neighboring amide carbonyl oxygen atom to generate isomünchnone-type intermediates. Subsequent 1,3-dipolar cycloaddition across the pendant olefin affords intramolecular cycloadducts in high yield. Exposure of these cycloadducts to boron trifluoride etherate results in a Lewis acid-induced ring opening to generate N-acyliminium ions which then undergo Mannich cyclization onto the neighboring pi-framework attached to the amide nitrogen atom. The cis stereochemistry of the resulting A/B ring fusion is analogous to similar erythrinane products obtained via a Mondon-enamide-type cyclization. The stereochemical assignment of the final cyclized products was determined by X-ray crystallography. Molecular mechanics calculations show that the ground state energy of the cis-fused diastereomer is 4.6 kcal lower than that of the trans diastereomer, and presumably some of this thermodynamic energy difference is reflected in the transition state for cyclization. In certain cases, proton loss from the initially formed N-acyliminium ion occurs prior to cyclization to give acyl enamides which subsequently cyclize producing epimeric products.

ChemInform Abstract: Remarkable Selectivity in Lewis Acid Induced Ring Opening of 5‐Acetyl‐ 10,11‐dihydro‐10,11‐epoxy‐5H‐dibenz(b,f)azepine.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Rearrangement studies on 3,3-bis(methylthio)-1-(arylcyclopropyl) -2-propen-1-ols: Synthesis of functionalized cyclopentenes and polyene esters

The cyclopropyl carbinols 8 and 9 obtained by either borohydride reduction (or Grignard addition) of the cyclopropyl ketones 1 are shown to undergo acid induced ring opening and intramolecular cyclization (5-exo or 6-endo) or deprotonation to afford either cyclopentene, biphenyl or conjugated polyene derivatives depending on the nature of Lewis acid, reaction conditions and the structuralfeatures present in the cyclopropyl carbinol. A probable mechanism for the formation of various products has been suggested.

A novel method for measurement of the merocyanine-spiropyran interconversion in non-activated 1, 3, 3-trimethylspiro- (2H-1-benzopyran-2, 2′-indoline) derivatives

A novel method for studying the merocyanine spiropyran (MC SP) interconversion is proposed: acid-induced ring opening of the SP followed by neutralization and stopped-flow measurement of ring closure of the resulting MC.

Aromatic substituent effect on the stereoselectivity of the gas-phase acid-induced ring opening in 9,10-oxides derived from trans-1,2,3,4,4a,10a-hexahydrophenanthrene

The effect of the aromatic ring substituents on the product distribution of the gas-phase acid-induced ring opening of benzocondensed epoxides 2a and 2b with MeOH was examined and compared with results from methanolysis. The observed syn/anti diastereoselectivity is strictly dependent on the type of the aromatic ring substituent (6-OCH 3 or 7-Br), and a very satisfactory Hammett-type linear correlation was found for both epoxides. A razionalization of the results is given.

Acid-induced ring opening of .alpha.-bis(methylthio)methylenealkyl cyclopropyl ketones: a novel route to substituted cyclopentanones through carbocationic cyclizations

α-[Bis(methylthio)methylene]alkyl2-styrylcyclopropyl ketones lOa-d,f and their higher enyl analogues 10e,g undergo acid-induced ring opening and carbocationic cyclizations to afford substituted cyclopentanone derivatives. The structures of these products depend on the reaction conditions and the nature of the substituent in the aryl ring. The methodology has been extended to the synthesis of 11-oxosteroid precursors 22 and 25.

Regioselectivity in the reactions of methoxydehydrobenzenes with furans. Part 2. 2-Methoxyfuran and methoxydehydrobenzenes

Acid-induced ring opening of adducts of furan and methoxydehydrobenzenes gives the naphthalenols derived from the more stable carbocation. The cycloadditions of methoxydehydrobenzenes containing a 3-methoxy group and 2-methoxyfuran are highly regiospecific. The adducts, being strained acetals, undergo ring opening to provide a convenient synthesis of naphthalenols.

Synthesis and Acid-induced Ring Opening of Modified Glycals. Synthons for (14 R,15 R)-Lipoxin B and (7 S,8 R)-( – )-Disparlure

The chiral 1,2-unsaturated dihydroxyaldehydes 7 and 11 were synthesized as synthons for (14R,15R)-lipoxin B 12 and (7S,8R)-( – )-cis-disparlure 13, based on new glycals 6 and 10 prepared from α-d-galactose.

Gas-phase acid-induced ring opening in diastereoisomeric 9,10-oxides derived from trans-1,2,3,4,4a,10a-hexahydrophenanthrene

The stereochemical outcome of the two diastereoisomeric rigid benzocondensed epoxides 2a and 2b in the acid-induced nucleophilic attack by MeOH in the gas-phase was studied and compared with the corresponding results obtained with the mobile epoxides of type 1. The stereochemistry of the ring opening process in these systems ( 1, 2a, b) appears to be dependent on the extent of the positive charge developed at the benzylic carbon. A rationalization which implies different benzylic carbocationic species is proposed, while the hypothesis of the intermediacy of fully developed benzylic carbenium ions does not appear to be supported by the present results.