Abstract:
Asymmetric Michael reactions of 1,4-naphthoquinones bearing a chiral auxiliary at C-2 1-4 with 2-trimethylsilyloxyfuran using various Lewis acids afforded the corresponding furofuran adducts 5-12. Moderate levels of diastereomeric excess were obtained using (R)-pantolactone, (S)-N-methyl-2-hydroxysuccinimide and (R)-(+)-4-benzyl-2-oxazolidinone as chiral auxiliaries. Low asymmetric induction was achieved using a camphorsultam auxiliary. X-Ray crystallographic analysis of the pantolactone adduct enabled determination of the absolute stereochemistry of all adducts obtained. Evidence that the TMS-furan addition occurs via a Michael reaction rather than a Diels-Alder cycloaddition is provided. (C) 1998 Elsevier Science Ltd. All rights reserved.