Synthesis and reactivity against Cp2TiCl of 4-isoprenyl-β-lactams. Trapping of N-titanoimidoyl radicals from cyanoformyl-2-azetidinones

Abstract

A Staudinger reaction between methoxyketene and two different imines formed from citral afforded, after chemical transformation, the (E/Z)-4-alkenylepoxy-2-azetidinones 2, 3 and 4. These compounds, by reaction with Cp2TiCl, did not cyclize to afford the expected polycyclic β-lactams, but the corresponding allylic alcohols 12, 13 and 15 were obtained instead. Unexpectedly, the treatment of cyanoepoxide (E)-3 with Cp2TiCl also gave the hydroxyl aldehyde (E)-14 whose formation suggests to us that a possible radical reduction of the cyano group might have occurred, and we lastly succeeded in the capture of the N-titanoimidoyl radicals. The behaviour observed for the isoprenoid side chain in the Staudinger reaction, the reactions with Cp2TiCl, as well as the trapping of N-titanoimidoyl radicals generated from benzocyanoformyl-2-azetidinones with the Ti(III) reagent, are discussed.