NMR studies on epoxidations of allenamides. Evidence for formation of nitrogen-substituted allene oxide and spiro-epoxide via trapping experiments

C. Rameshkumar, Hui Xiong, Michael R. Tracey, Craig R. Berry, Letitia J Yao, Richard P. Hsung

Research output: Contribution to journalArticlepeer-review

51 Scopus citations

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 languageEnglish (US)
Pages (from-to)1339-1345
Number of pages7
JournalJournal of Organic Chemistry
Volume67
Issue number4
DOIs
StatePublished - Feb 22 2002

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