A short stereoselective preparation of dienamides from cyclobutene compounds. Application in the synthesis of a new cyclohexene nucleoside

A short stereoselective synthesis of N-acylamino-1,3-dienes was developed s tarting from the cyclobutene lactam 8, which was obtained from 2-hydroxypyr idine by a photochemical electrocyclic reaction. The tert-butoxycarbonyl de rivative 17 was prepared to facilitate nucleophilic attacks to the carbonyl group, and the subsequent thermal ring opening provided dienes 18-21. One of these (20) was used in the synthesis of the cyclohexene nucleoside 30. A Diels-Alder reaction between diene 20 and maleic anhydride provided the en do-cycloadduct 22a. Three additional steps yielded amine 26. Construction o f the uracil moiety afforded intermediate 29. Cyclization and removal of th e protecting groups occurred in one step in the presence of ammonia, giving the target molecule 30. Diene 20 also underwent [4 + 2] cycloaddition with methyl acrylate to provide predominantly the endo-product 23a, regioselect ively.