Investigation of the mechanism for the preparation of 6-phenyl-2,4-dioxotetrahydropyrans by the potassium carbonate promoted condensation between acetoacetate esters and benzaldehyde.

Treatment of benzaldehyde and an acetoacetate ester with potassium carbonate in an alcohol solvent proceeds via γ-C-alkylation rather than α-C-alkylation resulting in the formation of 6-phenyl-2,4-dioxotetrahydropyran. Based upon results from deuterium exchange experiments, carbon-13 labeling experiments, (1)H NMR monitoring studies, and reactivity studies, our proposed mechanism for this reaction involves deprotonation at the α-carbon, intramolecular proton transfer to form a γ-anion, addition of the resulting γ-anion to the carbonyl carbon of benzaldehyde, and intramolecular transesterification.

6-Phenyl-oxane-2,4-dione.

The title compound, C11H10O3, is a phenyl-subsituted dihydro-pyran-dione in which the heterocycle adopts a boat conformation with the phenyl substituent canted 72.14 (5)° relative to the mean plane of the heterocycle.

Synthesis of palladium colloids within polydimethylsiloxane and their use as catalysts for hydrogenation.

The presence of unreacted silanes within cured polydimethylsiloxane (PDMS) leads to the reduction of tetrachloropalladate(II) ions, generating encapsulated palladium colloids. The resulting colloids had varied morphology and were typically less than 80 nm in size. The Pd/PDMS vessels, which contained 0.10±0.01% Pd, were effective catalysts for the hydrogenation of carbon-carbon multiple bonds for at least ten successive runs with no loss of catalytic activity, and the catalyst does not exhibit the same pyrophoric behavior as Pd on carbon after use in hydrogenation reactions. In addition, storage of previously used Pd/PDMS vessels for 6 months in air did not affect the catalytic activity, and the overall morphology of the catalysts after use was the same as those that have not been involved in catalytic reactions.

Multiple gene-mediated NAD(P)H-dependent aldehyde reduction is a mechanism of in situ detoxification of furfural and 5-hydroxymethylfurfural by Saccharomyces cerevisiae.

Furfural and 5-hydroxymethylfurfural (HMF) are representative inhibitors generated from biomass pretreatment using dilute acid hydrolysis that interfere with yeast growth and subsequent fermentation. Few yeast strains tolerant to inhibitors are available. In this study, we report a tolerant strain, Saccharomyces cerevisiae NRRL Y-50049, which has enhanced biotransformation ability to convert furfural to furan methanol (FM), HMF to furan di-methanol (FDM), and produce a normal yield of ethanol. Our recent identification of HMF and development of protocol to synthesize the HMF metabolic conversion product FDM allowed studies on fermentation metabolic kinetics in the presence of HMF and furfural. Individual gene-encoding enzymes possessing aldehyde reduction activities demonstrated cofactor preference for NADH or NADPH. However, protein extract from whole yeast cells showed equally strong aldehyde reduction activities coupled with either cofactor. Deletion of a single candidate gene did not affect yeast growth in the presence of the inhibitors. Our results suggest that detoxification of furfural and HMF by the ethanologenic yeast S. cerevisiae strain Y-50049 likely involves multiple gene mediated NAD(P)H-dependent aldehyde reduction. Conversion pathways of furfural and HMF relevant to glycolysis and ethanol production were refined based on our findings in this study.