Oxidative Rearrangement of Sulfur-Containing Tertiary Allylic Alcohols: Synthesis of 2-Cycloalkenones Bearing 3- and 3- Substituents

Article abstract of DOI:10.1021/jo00063a011

Substrate 1-<(phenylthio)methyl>-2-cycloalkenols 3a-d and 1-<2-alkyl-1,3-dithian-2-yl>cyclohexenols 1a-d were prepared by adding <(phenylthio)methyl>lithium and 2-lithio-2-alkyl-1,3-dithianes, respectively, in the 1,2-mode to various 2-cycloalkenones.The ranges of yields for the additions were 86-95percent in the (phenylthio)methyl series and 69-88percent in the dithiane series.A representative compound from each range of substrate tertiary allylic alcohols was then treated with a series of oxochromium(VI)-amine reagents such as pyridinium chlorochromate (PCC), pyridinium dichromate (PDC), the Collins reagent (CrO3*Pyr2), and 2,2'-bipyridinium ch lorochromate (BPCC).The oxochromium(VI)-amine reagents effected conversions of the representative substrates to the corresponding 3-<(phenylthio)methyl>- and 3-<2-alkyl-1,3-dithian-2-yl>-2-cycloalkenones 4a-d and 2a-d which were measured by gas chromatographic-mass spectral analysis.When comparing the efficiency of the range of oxochromium(VI)-amine reagents, PCC was found to give the best conversions to the corresponding transposed α,β-unsaturated carbonyl compounds in both series of substrates, while the Jones reagent gave only decomposed material and no recovery of substrate.Distinct improvements on the initial PCC protocol using silica gel as an in situ adsorbent and promotion by ultrasound were then established with a range of substrate tertiary allylic alcohols while comparing sonicated versus nonsonicated experiments.The isolated yields of transposed products were found to be increased as much as 60percent in the dithiane series and 9percent in the (phenylthio)methyl series with the application of high-intensity ultrasound.Prolonged exposure of the substrate (3a) in the (phenylthio)methyl series to the PCC/silica reagent system resulted in the recovery of the corresponding sulfone (5), the identity o f which was confirmed by selective oxidation of the transposed enone (4a) with m-chloroperbenzoic acid.