ASYMMETRIC INDUCTION IN THE OXIDATION OF [2.2]PARACYCLOPHANE-SUBSTITUTED SELENIDES - APPLICATION OF CHIRALITY TRANSFER IN THE SELENOXIDE [2,3] SIGMATROPIC REARRANGEMENT

When selenides derived from [2.2]paracyclophane systems were oxidized, the chiral aryl substituent provided for asymmetric induction to the new selenoxide chiral center. The ratio of diastereomeric selenoxides obtained depended upon whether the oxidation was performed under kinetic conditions or whether the selenoxides were allowed to equilibrate. Thus 4-(methylseleno)[2.2]paracyclophane (10) gave a 1:1 kinetic ratio of selenoxides 11 and 12 on oxidation with m-chloroperbenzoic acid and a 30:1 ratio at equilibrium (thermodynamic ratio). The more hindered 4-(methylseleno)-15-(p-toluenesulfonyl)[2.2]paracyclophane (23) was prepared in almost optically pure form. It gave a better kinetic ratio of selenoxides 24 and 25 (4.5:1) but a poorer thermodynamic one (1.5:1). The relative configuration of 11 and 12 and the absolute configuration of 24 and 25 were assigned. A geranyl selenide substituted with a resolved [2.2]paracyclophane substituent was oxidized and allowed to undergo a selenoxide [2,3] sigmatropic rearrangement to linalool. This sequence proves that the [2,3] sigmatropic rearrangement of gamma,gamma-dialkylallyl selenoxides proceeds through an endo transition state and illustrates the use of asymmetric induction during oxidation followed by chirality transfer by rearrangement to prepare optically active allylic alcohols.