Synthesis of carbo- and aza-bicyclo[4.3.0] and [4.4.0] compounds by Ti(II)-mediated cyclization of 2,7- or 2,8-enynyl-1-ol derivatives

The reaction of 2,7- and 2,8-enynyl-1-ol derivatives where the ene moiety is a part of a ring with a Ti(O-i-Pr)4/2 i-PrMgCl reagent proceeds smoothly with excellent stereoselectivity to afford carbo- or aza-bicyclo[4.3.0] and [4.4.0] compounds, respectively, in high yields.