ADDITION OF ALLYLSTANNANES TO AN OXY-STABILIZED CARBENIUM ION ON A 1,7-DIOXASPIRO[5.5]UNDECANE RING-SYSTEM

The nucleophilic addition of allylstannanes to -2-acetoxy-5-benzyloxy- 1,7-dioxaspiro[5.5]undecane 1 has been studied. The optimum conditions involve the use of trimethylsilyl trifluoromethanesulfonate in dichlo romethane at -78 degrees C. In the examples studied, substitution of t he acetoxy group at C-2 proceeds from an axial direction, however, sub sequent ring flipping of the substituted ring occurs as well affording allylated prod.,ts in which the substituents at both C-2 and C-5 are equatorial.