Cycloaddition reaction of Schiff bases with ketenes generated by pyrolysis of 2-aryl-substituted 1,5,7-trioxaspiro[2.5]octane-4,8-diones

摘要

The alpha-oxo ketenes 6 which are generated by the pyrolysis of the 2-aryl-substituted 1,5,7-trioxaspiro[2.5]octane-4,8-diones 1, were reacted with Schiff bases 2 to give spiro compounds constructed between the beta-lactam and 1,3-dioxolan-4-one; i.e., the 2,3,6-triaryl-2-aza-5,7-dioxaspiro[3.4]octane-1,8-diones 3 and 4. Hydrogenation of the mixture of 3a and 4a in the presence of catalytic amount of Pd-C produced the trans-2-benzyloxy-1,4-diphenyl-beta-lactam-3-carboxylic acid 9.