Baker's yeast reduction of cyclic δ-ketoesters: synthesis and chiroptical properties of condensed δ-lactones

Enantiomerically pure condensed δ-lactones have been prepared from the corresponding δ-ketoesters by the use of Saccharomyces cerevisiae. The reactions were not only highly enantioselective but also highly diastereoselective, provided the baker's yeast was preincubated at 50°C for 30 min. Interestingly, and contrary to what is usually found, the use of nutrients inhibited the bioreductions. The relative configurational assignments have been made by means of NMR, while the absolute configurations and conformations of the lactone rings were attributed by means of CD studies.     

Synthesis of enantiomerically pure bicyclic condensed δ-lactones via microbial reduction and enzymic resolution strategies

The formation of enantiopure δ-lactones condensed with alicyclic rings has been achieved either by reduction with baker's yeast of the corresponding δ-keto esters and δ-keto acids or by enzymic resolution of the former compounds. The absolute configurations of the lactones were determined by means of CD spectroscopy, using the correlation method.     

The configuration of δ-lactones formed by cyclization of geranylacetic acid

Summary The previously proposed configurations for the -lactones formed by cyclization of the geranylacetic acids have been considered and exchanged.     

Oxazaborolidinium ion-catalyzed cyclopropanation of α-substituted acroleins: enantioselective synthesis of cyclopropanes bearing two chiral quaternary centers

A catalytic synthetic route to highly functionalized chiral cyclopropane derivatives was developed by Michael-initiated cyclopropanation of α-substituted acroleins with aryl- and alkyl diazoacetates. In the presence of chiral (S)-oxazaborolidinium cation 1b as a catalyst, the reaction proceeded in high yield (up to 93%) with high to excellent diastereoselectivity (up to 98% de) and enantioselectivity (up to 95% ee).     

Vapour pressures and enthalpies of vaporization of a series of δ-lactones

Vapour pressures and molar enthalpies of vaporization of a series of δ-lactones (δ-valerolactone (CAS#542-28-9), δ-hexanolactone (CAS#823-22-3), δ-octanolactone (CAS#698-76-0), δ-nonanolactone (CAS#3301-94-8), and δ-decanolactone (CAS#705-86-2)) have been determined by the transpiration method. A linear correlation of enthalpies of vaporization ${\mathrm{\Delta }}_{\text{l}}^{\text{g}}{H}_{\text{m}}$ at T = 298.15 K of the δ-lactones studied with the number of carbon atoms has been found.     

Asymmetric synthesis of chiral δ-lactones containing multiple contiguous stereocenters

A versatile methodology for the asymmetric synthesis of chiral δ-lactones containing multiple contiguous stereocenters has been developed that relies on a series of Evans' aldol, hydroxyl-directed cyclopropanation, methanolysis, and Hg(II) mediated cyclopropane ring-opening reactions for stereocontrol.     

Expanding the utility of Brønsted base catalysis: biomimetic enantioselective decarboxylative reactions

As a result of the low reactivity of simple esters, the use of them as nucleophiles in direct asymmetric transformations is a long-standing challenge in synthetic organic chemistry. Nature approaches this difficulty through a decarboxylative mechanism, which is used for polyketide synthesis. Inspired by nature, we report guanidine-catalyzed biomimetic decarboxylative C-C and C-N bond-formation reactions. These highly enantioselective decarboxylative Mannich and amination reactions utilized malonic acid half thioesters as simple ester surrogates. It is proposed that nucleophilic addition precedes decarboxylation in the mechanism, which has been investigated in detail through the identification of intermediates by using electrospray ionization (ESI) mass-spectrometric analysis and DFT calculations.     

Synthesis of γ-sulfonyl δ-lactones and β-sulfonyl styrenes

A facile route to the synthesis of γ-sulfonyl lactones 5 and β-sulfonyl styrenes 6 has been developed, achieving moderate to good yields via the (1) NaH mediated Michael addition of β-ketosulfones 3 and methyl acrylate in refluxing THF and (2) NaBH₄ mediated stereoselective reduction/lactonization of δ-ketoesters 4 in boiling MeOH, or (3) boron trifluoride etherate mediated ring-opening of lactones 5 in MeOH at reflux.     

Kinetic resolution of β-lactams via enantioselective N-acylation

Enantioselective N-acylation of 4-aryl-β-lactams in the presence of acyl transfer catalyst Cl-PIQ provides an effective method for their non-enzymatic kinetic resolution.     

Asymmetric catalysis. Part 137: Nickel catalysed enantioselective α-ketol rearrangement of 1-benzoylcycloalkanols

Using catalytic amounts of Ni complexes the tertiary α-hydroxyketones 1-benzoylcyclobutanol 1 and 1-benzoylcyclopentanol 3 undergo α-ketol rearrangement. The use of the chiral ligand 2,6-bis[(4S)-isopropyl-2-oxazolin-2-yl]pyridine gave an enantiomeric excess of about 34% for both systems, forming (−)-2-hydroxy-2-phenylcyclopentanone 2 and (R)-(−)-2-hydroxy-2-phenylcyclohexanone 4. 1-Benzoylcyclohexanol 5 could not be catalytically rearranged to 6 under these conditions.     

The versatile roles of ammonium salt catalysts in enantioselective reduction and alkylation of α,β-unsaturated aldehydes: iminium catalysis, enamine catalysis and acid catalysis

A novel strategy for highly efficient utilization of chiral ammonium salt catalysts has been described in this paper. Three kinds of catalytic functions including iminium catalysis, enamine catalysis, and acid catalysis of chiral ammonium salt catalysts, have been achieved in the enantioselective reduction and alkylation reaction of α,β-unsaturated aldehydes with alcohols.     

Highly diastereo- and enantioselective aldol reaction of methyl α-isocyanoacetate: a cooperative catalysis approach

The cooperative catalyst activity between a chiral transition-metal catalyst and an achiral organocatalyst has been identified as one of the critical asymmetric reaction optimization components in the highly diastereo- and enantioselective aldol reaction of methyl α-isocyanoacetate.     

Asymmetric catalysis. Part 153: Metal-catalysed enantioselective α-ketol rearrangement

Promoted by catalytic amounts of Ni complexes tertiary α-hydroxyketones 1a, 3a–5a undergo rearrangement, forming chiral isomers 1b, 3b–5b. The best enantioselection was obtained with the model system 1-benzoylcyclopentanol 4a/2-hydroxy-2-phenylcyclohexanone 4b. In a ligand screening 2-[4-(S)-tert-butyloxazolin-2-yl]pyridine gave the highest enantiomeric excess of 46% (S)-4b. The analogous isomerisation reactions of α-hydroxyimines 6a, 7a forming chiral α-aminoketones 6b, 7b were established.     

Improved synthesis of α-Methylene-γ-lactones via organotin reagents

The products of the reaction between aldehydes and the organotin reagent (1) have been converted to the corresponding α-methylene-γ-lactones in excellent yield under extremely mild conditions.     

Synthesis of stereodefined fused δ-hydroxy-γ-lactones from dealkylative cyclization of epoxy-diesters

A dealkylative lactonization of stereodefined aryl-substituted epoxides allows the preparation of densely functionalized fused δ-hydroxy-γ-lactones having three consecutive stereochemically defined stereocenters.     

γ-Lactones from δ-lactones: total synthesis of the biosynthetic derailment product mupirocin H

Two different strategies for the synthesis of functionalised γ-lactones from δ-lactones are described and used in a convergent synthesis of (+)-mupirocin H. The total synthesis is versatile and may be readily adapted for the preparation of further truncated metabolites from Pseudomonas fluorescens.