Stereoselective addition of benzonitrile oxide and N-benzyl-C-phenylnitrone to (5RS,6SR)-5,6-dihydro-6-ethyl-5-methylpyran-2(2H)-one. Crystal structure of (1RS,4RS,5RS,6RS,9SR)-8-benzyl-1,5-dimethyl-4-ethyl-9-phenyl-3,7-dioxa-8-azabicyclo [4.3.0]nonan-2-one.

Abstract

Addition of benzonitrile oxide and N-benzyl-C-phenylnitrone to (5RS,6SR)-6-ethyl-5,6-dihydro-5-methyl-2H-pyran-2-one (4) took place stereoselectively syn to the allylic methyl substituent. Methylation of the nitrone adducts (7) and (8) using lithium di-isopropylamide and methyl iodide involved retention of configuration at C-1 although a small amount of ring-opening and closing occurred in the latter case to give the methylated isoxazolidine (11) as a minor product. The structure of (1RS,4RS,5RS,6RS,9SR)-8-benzyl-4-ethyl-1,5-dimethyl-9-phenyl-3,7-dioxa-8-azabicyclo[4.3.0]nonan-2-one (10) was confirmed by an X-ray structure determination.