Reaction of 2H-Azirine-Phosphine Oxides and -Phosphonates with Enolates Derived from β-Keto Esters

Cyclopenta[b]-pyrrole-2-phosphine oxides 4a and -phosphonates 4b,c are generated by the addition of cyclic enolates derived from ethyl 2-oxo-cyclopentanecarboxylate 2 to phosphorated 2H-azirines 1. However, the addition of enolate derived from acyclic 2-oxo-butanoate 10 to 2H-azirine phosphine oxide 1 led to vinylogous N-acyl-α-aminoalkyl phosphine oxides 12, involving the carbonyl group and the Cα of the keto ester 10. Ring closure of vinylogous derivative 12 in the presence of base afforded pyrrole-2-phosphine oxide 11. The addition of enolates derived from indenone-carboxylate 15 to 2H-azirines 1 led to the formation of functionalized N-substituted 1H-benzo[d]azepine derivatives 17.