Abstract
Two epoxidations of chiral allenamides are described here. While treatment with m-CPBA led to highly stereoselective formation of an α-keto aminal that can be useful synthetically, DMDO oxidation led to conclusive evidence for both nitrogen-substituted allene oxide (via mono-epoxidation) and spiro-epoxide (via bis-epoxidation) using intramolecular nucleophilic trapping experiments. NMR studies provide reliable evidence for a 3-oxetanone that can be derived from the spiro-epoxide and also suggest the presence of an allene oxide. Despite a facile second epoxidation as evidenced by the predominant formation of the 3-oxetanone, in the presence of furan, [4 + 3] cycloaddition of the nitrogen-substituted allene oxide or oxyallyl cation with furan occurs faster than the second epoxidation efficiently leading to cycloadducts. This rate difference plays an invaluable role for the success of a stereoselective sequential epoxidation-[4 + 3] cycloaddition reaction via DMDO epoxidations of chiral allenamides.
Original language | English (US) |
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Pages (from-to) | 1339-1345 |
Number of pages | 7 |
Journal | Journal of Organic Chemistry |
Volume | 67 |
Issue number | 4 |
DOIs | |
State | Published - Feb 22 2002 |