REGIO-SELECTIVITY AND DIASTEREOSELECTIVITY IN THE REACTION SEQUENCE FROM SECONDARY 3-OXA-5-HEXEN-1-YLAMINES TO BICYCLIC COMPOUNDS VIA NITRONES

Secondary amines 2 and 8 are oxidized by hydrogen peroxide in the pres ence of sodium tungstate providing nitrones. If the amino function is substituted by one primary and one secondary alkyl moiety, oxidation p roceeds with high regioselectivity at the primary alkyl group affordin g aldonitrones. Thus, compound 2b gives exclusively 3b that undergoes an intramolecular cycloaddition yielding 4b. From 2c, however, in addi tion to 4c nitrone 5 is formed as by-product, which affords the bridge d compound 6 on heating in toluene. Oxidation of compounds 8 yields ni trones 9 which are converted to bridged compounds 10 as major products along with small amounts of regioisomers 11 at elevated temperatures. The intramolecular cycloaddition of the chiral nitrones 3b and c as w ell as 9b proceeds with high diastereoselectivity.