Lewis acid promoted intramolecular (3 + 2) 'cycloadditions' of methyleneaziridines with alkene and alkyne acceptors |
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Authors: | Griffin Karen Montagne Cyril Hoang Cam Thuy Clarkson Guy J Shipman Michael |
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Institution: | Department of Chemistry, University of Warwick, Gibbet Hill Road, Coventry, UK CV4 7AL. |
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Abstract: | 2-Methyleneaziridines can be tethered to a variety of alkene or alkyne acceptors through the saturated carbon of the heterocyclic ring by application of a simple lithiation/alkylation sequence (8 examples, 31-59%). Treatment of the resultant alkene bearing substrates with BF(3)·OEt(2) leads to cis-octahydrocyclopentac]pyrroles in which up to four contiguous stereocentres are created in a diastereocontrolled manner after reductive work-up. Using an alkyne based substrate, a 2,4,5,6-tetrahydrocyclopentac]pyrrole is produced by rapid tautomerisation of the initially formed bisenamine. Evidence that these (3 + 2) 'cycloadditions' proceed in a stepwise manner via a 2-aminoallyl cation is presented. |
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