Benzyl alcohols Pummerer rearrangement

DMSO or other sulfoxides react with trimethylchlorosilanes (TCS) 14 or trimefhylsilyl bromide 16, via 789, to give the Sila-Pummerer product 1275. Rearrangement of 789 and further reaction with TCS 14 affords, with elimination of HMDSO 7 and via 1276 and 1277, methanesulfenyl chloride 1278, which is also accessible by chlorination of dimethyldisulfide, by treatment of DMSO with Me2SiCl2 48, with formation of silicon oil 56, or by reaction of DMSO with oxalyl chloride, whereupon CO and CO2 is evolved (cf also Section 8.2.2). On heating equimolar amounts of primary or secondary alcohols with DMSO and TCS 14 in benzene, formaldehyde acetals are formed in 76-96% yield [67]. Thus reaction of -butanol with DMSO and TCS 14 gives, via intermediate 1275 and the mixed acetal 1279, formaldehyde di-n-butyl acetal 1280 in 81% yield and methyl mercaptan (Scheme 8.26). Most importantly, use of DMSO-Dg furnishes acetals in which the 0,0 -methylene group is deuter-ated. Benzyl alcohol, however, affords, under these reaction conditions, 93% diben-zyl ether 1817 and no acetal [67]. 

Further elaboration of the sulfur cycloadducts could be achieved by the use of a Pummerer rearrangement in the syntheses of 5-(hydroxymethyl)prolines. Oxidation of adduct 298 to sulfoxide 299, followed by treatment with TEA in DCM and quenching with either methanol or benzyl alcohol, delivered the Pummerer products 300 in 57% yield for R = Me and 38% for R = Bn as single diastereoisomers. Raney Ni desulfurization and Pearlman s catalyst mediated hydrogenolysis, for R = Bn furnished the final enantiopure proline derivative (Scheme 3.99). 

The one-pot reaction of the a-(difluoromethyl)-p-sulfinylenamine 70 with trifluoroacetic anhydride in CHCI3, followed by treatment with silica gel affords 4-(difluoromethyl)-5-p-tolylthio-2(3//)-oxazolone 74 (Fig. 5.18). This reaction proceeds via a Pummerer-type rearrangement, followed by [l,3]-proton shift and the simultaneous elimination of trifluoroacetic acid and benzyl alcohol. ... 

The use of trimethylsilyl halides has been expanded further to afford optically pure benzyl alcohols through a stereoselective vinylogous Pummerer rearrangement. The reaction proceeds via a l,4 migration of the sufinyl oxygen atom to give (i )-benzyl alcohols 30a-f with > 98% ee. 

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