Studies on a New Access to Z-Ethylenic Pseudodipeptides Based on Ring-ClosingMetathesis: Obtention and Reductive Cleavage of N-ArylsulfonylDihydropyridones

In the reaction with tert-butyloxycarbonyl anhydride (Boc2O), N-(o-vinylacetyloxy)benzenesulfonyl allylic amines 4a-c undergo concomitant O to N acyl migration to give N-(o-vinyl­acetyloxy)-N-(o-tert-butoxycarbonyloxy)benzenesulfonyl allylic amines 16a-c. In the presence of Grubbs’ second-generation catalyst, 16a-c are converted into N-arylsulfonyl-3,6-dihydropyridones 17a-c. The Boc group was removed from 17b and the resulting 18 was reductively cleaved with LiAlH4 to the ring-opened N-arylsulfonylamino alcohol 20 and with DIBAL to the ring-opened N-arylsulfonylamino aldehyde 21 that are close N-protected precursors of the Z-ethylenic pseudopeptidic analogue of l-Phe-Gly.