INVESTIGATIONS ON 1,2-ASYMMETRIC, 1,3-ASYMMETRIC, AND 1,4-ASYMMETRIC INDUCTION IN INTRAMOLECULAR REFORMATSKY REACTIONS PROMOTED BY SAMARIUM(II) IODIDE

A series of beta- and gamma-haloacetoxy ketones and aldehydes bearing substituents at various positions were cyclized with samarium(II) iodide (SmI2), providing the corresponding hydroxy lactones. Excellent 1,2- and 1,3-asymmetric inductions were demonstrated in the cyclization of beta-haloacetoxy carbonyl substrates. Although 1,2-asymmetric induction was also exceptional with the gamma-bromoacetoxy ketones, 1,3-asymmetric induction was in general far less impressive. Low levels of 1,4-asymmetric induction were achieved in cyclization of the gamma-haloacetoxy substrates. Despite the varying levels of asymmetric induction demonstrated with the gamma-haloacetoxy substrates examined, this method provides a useful, general route to stereodefined 4-hydroxy-1-oxacyclohexan-2-ones and 4-hydroxy-1-oxacycloheptan?? -2-ones, which can be carried out under very mild conditions.