Giuseppe Bellucci

CROWN ETHER CATALYZED STEREOSPECIFIC SYNTHESIS OF Z- AND E-STILBENES BY WITTIG REACTION IN A SOLID-LIQUID TWO-PHASES SYSTEM

Abstract Potassium hydroxide and a catalytic amound of 18-crown-6 are used, in alternative to the classical Wittig conditions, to prepare very rapidly and stereoselectively Z- and E-stilbenes. In particular, the use of benzyltriphenylphosphonium iodides always leads to a complete Z- stereospecificity, while benzyldiphenylchlorophosphonium salts give a complete E-stereospecificity.

A SIMPLE AND HIGHLY DIASTEREOSELECTIVE PREPARATION OF GLYCAL EPOXIDES USING THE MCPBA-KF COMPLEX

Abstract Glycals are converted to the corresponding epoxides in high yields by a diastereoselective one-step epoxidation using the m -chloroperoxybenzoic acid-KF complex in anhydrous dichloromethane.

Different enantioselectivity and regioselectivity of the cytosolic and microsomal epoxide hydrolase catalyzed hydrolysis of simple phenyl substituted epoxides

Abstract The cytosolic (cEH) and the microsomal epoxide hydrolase (mEH) hydrolyse styrene oxide and trans -1-phenylpropene oxide with different enantioselectivity and regioselectivity. While mEH always leads to a regiospecific and enantioselective opening at the non-benzylic oxirane carbon, cEH gives a non-regioselective and non-enantioselective attack to styrene oxide and a regiospecific and non-enantioselective attack at the benzylic carbon of 1-phenylpropene oxide.

Enantioconvergent transformation of racemic cis-β-alkyl substituted styrene oxides to (R,R) threo diols by microsomal epoxide hydrolase catalysed hydrolysis

Abstract Both enantiomers of cis-β-ethyl, β-n-propyl, β-n-butyl, and β-n-hexyl substituted styrene oxides undergo microsomal epoxide hydrolase catalysed hydration at the (S) carbon to give the corresponding (R,R) threo diols in a > 90% e.e. A complete kinetic resolution of the racemic epoxide is also obtained with the β-ethyl substituted substrate, but not with its higher homologues.

Substrate enantioselectivity m the rabbit liver microsomal epoxide hydrolase catalyzed hydrolysis of trans and cis 1-phenylpropene oxides. A comparison with styrene oxide

Abstract A preferential consumption of the (1S,2S) enantiomer of (±)- trans -,1-phenylpropene oxide ( 3 ) and of the (1R,2S) enantiomer of cis -1-phenylpropene oxide (5) is observed during the rabbit liver mEH catalyzed hydrolysis of these epoxides. This preference is, respectively, much lower and much higher than that found for the consumption of the (R) enantiomer in the hydrolysis of (±)-styrene oxide. These results are rationalized in terms of the K M and V max of the respective reactions.

Enantioconvergent transformation of racemic cis-dialkyl substituted epoxides to (R,R) threo diols by microsomal epoxide hydrolase catalysed hydrolysis

Abstract Both enantiomers of (±)-9,10-epoxystearic acid ( 1b ), cis -(±)-5,6-epoxyhexadecane ( 1c ) and cis -(±)-11,12-epoxyhexadecan-1-ol ( 1d ) as well as the meso cis -9,10-epoxyoctadecane ( 1a ) undergo microsomal epoxide hydrolase catalyzed hydration at the (S) carbon to give the corresponding (R,R) threo diols in a >90 e.e.

The epoxide hydrolase catalyzed hydrolysis of trans-3-bromo-1,2-epoxycyclohexane. A direct proof for a general base catalyzed mechanism of the enzymatic hydration.

Abstract The hydrolysis of (±)- trans -3-bromo-1,2-epoxycyclohexane in the presence of rabbit liver microsomes was investigated, and found to yield, beside c -3-bromocyclohexane- r -1, t -2-diol, 2,3-epoxycyclohexanol. It was demonstrated that the latter compound was the only product of the enzymatic reaction, whereas the diol resulted from a non enzymatic hydration in the reaction medium. These data provide the first direct proof for a general base catalysis in the enzymatic epoxide hydration, previously hypothesized on the basis of several lines of indirect evidence, and disprove alternative mechanisms involving protonation of the oxirane oxygen.

Kinetic resolution by epoxide hydrolase catalyzed hydrolysis of racemic methyl substituted methylenecyclohexene oxides

Abstract A complete kinetic resolution of 2,2-dimethylmethylenecyclohexene oxide and a partial resolution of the cis and trans -2-methylmethylenecyclohexene oxides, but not of their 3-methyl substituted isomers, have been achieved by partial hydrolysis to the corresponding diols using the microsomal epoxide hydrolase. No substrate enantioselectivity was in found for the hydrolysis of all these substrates by the cytosolic epoxide hydrolase.

Diastereoselective bromination of allyl glycosides using tetrabutylammonium tribromide

Abstract Both (R) and (S)-2,3-dibromo-1-propanol with e.e. up to 60% have been obtained by diastereoselective addition of Br 2 to allyl glucosides and galactosides having only one unprotected hydroxyl group at C-2 or C-6 using tetrabutylammonium tribromide, followed by hydrolysis. The absolute configuration is shown to depend on the position of the free hydroxyl and on the configuration at the anomeric centre.

Bromination of 3-cyclohexene-1-carboxylic acid, epoxydation of methyl 3-cyclohexene-1-carboxylate and opening of methyl cis- and trans-3,4-epoxycyclohexane-1-carboxylate:Stereochemical results

Abstract Bromination of 3-cyclohexene-1-carboxylic acid ( 1 ) gives mixtures of the trans -dibromo-derivatives 3 and 4 and cis -3-hydroxy- trans -bromocyclohexane-1-carboxylic acid lactone ( 5 ). Lactone 5 is obtained by brominating 1 in the presence of triethylamine, showing that halogen preferentially attacks the double bond anti with respect to the carboxyl group. Epoxydation of the methyl ester of 1 also takes place prevalently anti to the methoxycarbonyl group. Ring opening of methyl cis -3,4-epoxycyclohexane-1-carboxylate ( 7 ) with hydrogen bromide gives methyl trans -3-bromo- cis -4-hydroxy- ( 13 ) and cis -3-hydroxy- trans -bromocyclohexane-1-carboxylate ( 6 ). Similar opening of methyl trans -3,4-epoxycyclohexane-1-carboxylate ( 11 ) affords methyl trans -3-hydroxy- cis -4-bromocyclohexane-1-carboxylate ( 14 ). The steric course of these reactions is ascribed to the effect of the electron-withdrawing substituent.