The 1.3 dipolar cycloaddition of alkynes 4–4 with acyclic nitrones, 1–3, 23 and 24 as well as with cyclic nitrones 27 is studied. As was found for the reaction of the aldonitrones 1–3 an increased portion of 5-regioisomers is formed with increasing steric demand of either of the two substituents, the C-alkyl substituent R9 and the N-alkyl substituent R1. Thus the conclusion if drawn that cycloaddition of 1–3 proceeds not only via transition states arising ...
