RESUMO
Lipase/metal nanobiohybrids, generated by growth of silver or gold nanoparticles on protein matrixes are used as highly effective dual-activity heterogeneous catalysts for the production of enantiomerically enriched 2,5-dihydrofurans from allenic acetates in a one-pot cascade process combining a lipase-mediated hydrolytic kinetic resolution with a metal-catalyzed allene cycloisomerization. Incorporating a novel strategy based on enzyme-polymer bioconjugates in the nanobiohybrid preparation enables excellent conversions in the process. Candida antarctica lipase B (CALB) in combination with a dextran-based polymer modifier (DexAsp) proved to be most efficient when merged with silver nanoparticles. A range of hybrid materials were produced, combining Ag or Au metals with Thermomyces lanuginosus lipase (TLL) or CALB and its DexAsp or polyethyleneimine polymer bioconjugates. The wider applicability of the biohybrids is demonstrated by their use in allenic alcohol cyclizations, where a variety of dihydrofurans are obtained using a CALB/gold nanomaterial. These results underline the potential of the nanobiohybrid catalysis as promising approach to intricate one-pot synthetic strategies.
RESUMO
Cu/TEMPO catalyst systems are known for the selective transformation of alcohols to aldehydes, as well as for the simultaneous coupling of alcohols and amines to imines under oxidative conditions. In this study, such a Cu/TEMPO catalyst system is found to catalyze the N-formylation of a variety of amines by initial oxidative activation of methanol as the carbonyl source via formaldehyde and formation of N,O-hemiacetals and oxidation of the latter under very mild conditions. A vast range of amines, including aromatic and aliphatic, primary and secondary, and linear and cyclic amines are formylated under these conditions with good to excellent yields. Moreover, paraformaldehyde can be used instead of methanol for the N-formylation.