Horacio F. Olivo

Lipase-mediated epoxidation utilizing urea–hydrogen peroxide in ethyl acetate

A green method for alkene epoxidation based on the chemo-enzymatic perhydrolysis of carboxylic acids and esters has been optimized using Novozyme 435, the immobilized form of Candida antarctica lipase B, and the complex urea–hydrogen peroxide (UHP). UHP, an anhydrous form of hydrogen peroxide, has the potential of releasing hydrogen peroxide in a controlled manner and thus avoids the need to add the aqueous hydrogen peroxide slowly to the reaction mixture. The absence of water in the reaction media was also beneficial, because it minimized undesired reactions of the oxidized products. A minimum amount of enzyme was necessary to show the catalytic effect. On recycling, the enzyme maintained its activity up to six rounds of epoxidations. A range of alkenes was epoxidized by this method providing yields ranging from 75 to 100 percent.

Baeyer–Villiger oxidation of substituted cyclohexanones via lipase-mediated perhydrolysis utilizing urea–hydrogen peroxide in ethyl acetate

A green method for Baeyer–Villiger oxidation based on the chemo-enzymatic perhydrolysis of carboxylic acids and esters has been optimized using Novozyme-435, the immobilized form of Candida antarctica lipase B, and the complex urea–hydrogen peroxide (UHP) in ethyl acetate. This protocol previously employed for the chemo-enzymatic epoxidation of unfunctionalized olefins was shown to be effective for the Baeyer–Villiger oxidation of cyclohexanone and substituted cyclohexanones. The absence of water in the reaction media avoided any hydrolysis of the oxidized product. A minimum amount of enzyme was necessary to show the catalytic effect. The reaction yields of substituted e-caprolactones varied depending on the nature of the substituent.

Indene-Based Thiazolidinethione Chiral Auxiliary for Propionate and Acetate Aldol Additions

An indene-based thiazolidinethione chiral auxiliary was prepared in two steps from trans-1-amino-2-indanol. Chlorotitanium enolates of this chiral auxiliary delivered excellent diastereoselectivities in propionate and acetate aldol additions. The chiral auxiliary was easily removed to deliver several valuable functionalities.

Synthesis of the C10-C17 fragment of aurisides and callipeltosides

Abstract The key unsaturated chiral C10–C17 fragment common on the synthesis of aurisides and callipeltosides was synthesized in six steps from 5-bromopentadienal via aldol condensation with Nagaos chiral auxiliary and further manipulation using Ohiras reagent and Negishis carboalumination–iodination.

Enzyme-catalysed kinetic resolution of 4-endo-hydroxy-2-oxabicyclo[3.3.0]oct-7-en-3-one and employment of the pure enantiomers for the synthesis of anti-viral and hypocholestemic agents

The endo-hydroxylactone (+/-)-(1) was resolved by enantioselective acetylation using Candida cylindracea lipase or preferentially Pseudomonas fluorescens lipase (pfl). Alternatively the corresponding butyrate (+/-)-(3) was hydrolysed with pfl to give the ester (+)-(1S,4R,5S)-(3) and the alcohol (-)-(1R,4S,5R)-(1). The latter compound was converted into carbovir (-)-(1R,4S)-(12) while the ester (+)-(3) was transformed into the delta-lactone (+)-(3R,5S)-(18). The exo-hydroxylactone (+/-)-(2) was resolved less efficiently by a trans-esterification process employing pfl and vinyl acetate.

Synthesis and microbial hydroxylation of some azabicycloalkanes

Abstract N -Substituted 7-azabicyclo[2.2.1]heptanes have been synthesized in a short route. These compounds containing benzamide or benzenesulfonamide groups are good substrates for microbial oxidation of unactivated carbons by B. bassiana .

RECENT SYNTHESES OF EPIBATIDINE. A REVIEW

INTRODUCTION .............. ........................... ..................................................................... ...... 3 I. CYCLOADDITION REACTIONS ............................................................................ ... .. .... 4 1. Diels-Alder Cycloaddi~o ................................................................................................ 4 2. [3+2] Dipolar Cycloadmbons .......................................................................................... 8 II. INTRAMOLECULAR NUCLEOPHILIC DISPLACEMENT REACTIONS.. .. . . . . . . . . . .9 111. RADICAL CYCLIZATION STRATEGIES .......................................... ....................... 20 IV. CONCLUSIONS ............................................................................................................... 22 REFERENCES ........................................................................................................................ 22 ..

Efficient Microwave Assisted Syntheses of 2,5-Diketopiperazines in Aqueous Media

Aqueous in situ one-pot N-Boc-deprotection-cyclization of Nα-Boc-dipeptidyl-tert-butyl and methyl esters under microwave irradiation afforded 2,5-diketopiperazines (DKPs) in excellent yields. This protocol is rapid, safe, environmentally friendly, and highly efficient, and showed that the tert-butoxy moiety is also an excellent leaving group for these cyclizations.

Enantioselective synthesis of the hydroxy-lactone moiety of mevinic acids

Abstract 2-Oxa-4 endo -hydroxybicyclo[3.3.0]-oct-7-en-3-one was resolved with Pseudomonas fluorescens lipase and one of the enantiomers was converted into a key intermediate in the synthesis of mevinic acids.

Chemoselective aromatic C-H insertion of α-diazo-β-ketoesters catalyzed by dirhodium(II) carboxylates.

The ability of α-diazo-β-ketoesters bearing a substituent on the benzylic position to undergo aromatic C-H insertion is described. Good to excellent yields of the aromatic C-H insertion products were observed with Rh(2)(tpa)(4) or Rh(2)(esp)(2) catalysts. This is an attractive strategy to prepare tetralins carrying a methyl group on the benzylic position, a structural motif found in several types of natural products.