Organic synthesis by the Pummerer reaction. II. Synthesis of .alpha.-hydroxy acid derivatives from .beta.-keto sulfoxides

Nucleophilic substitution at tricoordinate sulfur

“…174 Both substituent and solvent effects on the rearrangement of 2,6-dimethylbenzenesulfinate178 and trityl 2-methylbenz-enesulfinate175 point to an ionic mechanism which could involve either recombination of dissociated ions or an ion pair mechanism (eq 92). The trityl carbonium ion formed in the rearrange-RSOOR' RSOÓHR' -RS02" + H+ + +R' + (92) RS02-+ R' -RS02R' ment of trityl 2-methylbenzenesulfinate can be diverted to trityl azide if the rearrangement is carried out in the presence of tetra-rt-butylammonium azide. 175 Cope and his co-workers showed179 that the same mixture of a-methylallyl and crotyl phenyl sulfones was obtained from either -methylallyl or crotyl benzenesulfinate.…”

Chemical synthesis of (24R)-24,25-dihydroxy[26,27-3H]vitamin D3 of high specific activity

“…The synthesis of (24R)-24,25-(OH)2[26,27-3H]D3 (9a) (Figure 1) proceeded from 3/3-(tetrahydropyranyloxy)-5cholenic acid methyl ester (lb) which was obtained from the readily available 3/3-hydroxy-5-cholenic acid methyl ester (la) with 2,3-dihydropyran in dichloromethane and p-toluenesulfonic acid as catalyst. Homologation with simultaneous -hydroxylation of lb was achieved by the Pummerer rearrangement of the corresponding /3-keto sulfoxide 2 (Pummerer, 1909;Corey & Chajkovsky, 1962;Irinchijima et al, 1974Irinchijima et al, , 1975. Ester lb was converted to the /3-keto sulfoxide 2 with the methylsulfinyl carbanion formed from phenyl methyl sulfoxide, n-butyllithium, and diisopropylamine in anhydrous tetrahydrofuran.…”

Selective reduction of .alpha.-keto acids to .alpha.-hydroxy acids by phosphites

“…Pentaco- o' 5 valent species 6a and 6b have actually been isolated. 6 Alkaline hydrolysis of either 4 and/or 5 probably produces the a-hy-…”