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Abstract
Recently a new method for α-alkylation of carbonyl compounds, by way of cyclopropanation of their enol ethers and acid-catalyzed hydrolysis of the resultant cyclopropyl ethers, was introduced and applied to a stereospecific angular methylation1 and to the general construction of acyl, quaternary carbon sites.2 The following transformation of ketol, a degradation product of manool,3 into δ8(9)-sandaracopimaradiene (4b),4,5 represents another example of the power of the new synthetic method. In view of a former synthesis of manool3 and the recent interconversion of 4b with isopimaradiene (2a) and sandaracopimaradiene (2b)5 the experiments discussed below complete the total synthesis of the two natural, diterpenic hydrocarbons.6