Reaction Manifolds of Alkenes with benzene: Stereospecific syn-1,2-Ditosyloxylation of the Carbon-Carbon Double Bond and Other Processes

Article abstract of DOI:10.1021/jo00187a032

The treatment of various alkenes with benzene (1) in CH2Cl2 gives moderate yields of the corresponding vic-bis(tosyloxy)alkanes (2).When cis- and trans-2-butenes, cis- and trans-2-pentenes, cis-3-hexene, cis-4-octene, and cyclohexene are reactants, the tosyloxy ligands are introduced with syn stereospecifity.With cis- and trans-stilbenes, however, a mixture of meso- and dl-1,2-diphenyl-1,2-bis(tosyloxy)ethanes results from either alkene.Some alkenes react with 1 in a different way.Thus, trans-3-hexene and trans-4-octene with 1 give low yields of 2,5-bis(tosyloxy)-3-hexene and 3,6-bis(tosyloxy)-4-octene, respectively.Evidence is presented that the formation of the bis(tosyloxy)alkenes proceeds via initial oxidation of the trans alkenes by 1 to conjugated dienes and subsequent conjugate ditosyloxylation of the dienes.In a few cases, molecular rearrangements occur.Thus, norbornene with 1 gives 2,7-bis(tosyloxy)norbornane, among other products, while 1,1-diphenylethylene gives deoxybenzoin (major product) and (β,β-diphenylethenyl)phenyliodonium tosylate.The reaction of styrene with 1 depends on the medium; when CH2Cl2 is present, the product is 1-phenyl-1,2-bis(tosyloxy)ethane, but in the absence of solvent, the product is 1,1-bis(tosyloxy)-2-phenylethane.Most alkenes react with 1 to give p-toluenesulfonic acid as a byproduct, and, in rare instances, (iodoxy)benzene is obtained.A mechanism for the vic-ditosyloxylation of alkenes by 1, consistent with the observed syn stereospecificity, is proposed.