Enantioselective Reduction of Electrophilic C?C Bonds with sodium tetrahydroborate and ?semicorrin? cobalt catalysts
作者:Marian Misun、Andreas Pfaltz
DOI:10.1002/hlca.19960790404
日期:1996.6.26
‘Semicorrin’ cobaltcomplexes, prepared in situ from cobalt(II) chloride and the corresponding ligands, are efficient catalysts for the enantioselective reduction of electrophilic CC bonds with NaBH4. The best selectivities (> 90% ee) are achieved with α,β-unsaturated carboxamides and carboxylates. Analogous α,β-unsaturated nitriles, sulfones, and phosphonates afford enantiomeric excesses of 50–70%
In the pyroglutamicacid series, β-enaminoesters 3 were formed in the 2-position by opening of the corresponding Meldrum's derivative 6, and β-enaminonitriles 4 were obtained by treating carbamate vinylogous 5 by trimethytsilyl iodide. Alkylation and acylation of β-enaminoester 3a was briefly examined.