Efficient synthesis of (1R,4S,6R)-4-Isopropenyl-1,3,3-trimethyl-7-oxabicyclo[4.1.0]heptan-2-one

A simple and convenient one-pot synthesis of (1R,4S,6R)-4-isopropenyl-1,3,3-trimethyl-7-oxabicyclo[4.1.0]heptan-2-one was developed consisting in a thermodynamic methylation of carvone (NaH, MeI, THF, 20°C) followed by the epoxidation with alkalinized hydrogen peroxide. The reduction of the obtained epoxyketone with sodium borohydride proceeded stereoselectively to give a β-alcohol. The attempts to convert its isopropenyl fragment into an acetate group by a rearrangement of products or intermediates of the oxidative fragmentation resulted only in obtaining intermediate acyl derivatives.