Wittig rearrangement sulfones

Asymmetric induction of the same kind controls the configuration at the allylic methine carbon in compound (134) (134) results from a chain-elongating Wittig rearrangement (mechanism Scheme 6) of sulfone (133 equation 35). Surprisingly, the sense of the asymmetric induction in the rearrangement of silyl ether (135 equation 36) is opposite to that of more than a dozen other ( )-ethers. ... 

Bruckner s approach started from L-arabinose converted in five steps to allylic alcohol 175, and to alkoxy sulfone 176 thereafter (Scheme 23). Key [2, 3] Wittig rearrangement of lithiated 176 in the presence of allyl lithium led to the desired compound 178 and its C17 isomer (ratio 1.4 1) via the intermediate 177. Regioselective epoxidation and thiophenate epoxide ring opening furnished sulfide 179 transformed in four steps to the C14-C20 building block 180. 

These amidines have been extensively applied to dehydrohalogenation in organic synthesis and in some cases DBU (1) is more effective than DBN (2) [5]. A double bond can be also introduced into organic molecules by elimination of sulfonate ester instead of the halogen atom (i.e. dehydrosulfonation in addition to dehydrohalogenation). Furthermore, these amidines can be applied to the Wittig reaction [6], aldol condensation [6], 1,3-allyl rearrangement [7] and epimerization of the (3-lactam skeleton (at Ce of the penicillic acid derivatives). Sterically hindered phenols (e.g. 2,6-di(ferf-butyl)-4-fluorophenol) are (9-acetylated with DBU (1), which is superior to sodium hydroxide in the synthesis [8]. 

Dienes, as the simplest polyene systems, are widely encountered in sex pheromones like (4E, 7Z)-4,7-tridecadienyl acetate (100), a component of the sex pheromone of the potato tuberworm moth (Phthorimaea operculella). This compund was synthesized by Kim and Park [54] starting from a protected 5-hexen-l-ol and utilizing the chemistry of thio-substituted phosphonates (Scheme 28). Thus, the Pummerer rearrangement of a-phosphoryl sulfoxide 101 with 5-hexenyl acetate 102 afforded 7-acetoxy-l-methylthiohept-3-enyl phos-phonate 103 as an E/Z=85 15 mixture, being unreactive in the Horner-Wittig reaction, even after OAc deprotection/THP reprotection. However, the reaction of the more reactive a-phosphoryl sulfone 104 with w-hexanal successfully led to the required 1,4-diene 105, as an ElZ = 70 30 mixture, in 86 % yield. The final pheromone 100 was obtained after the desulfonylation of 105 with sodium hydrosulfite and the OTHP OH OAc deprotection/reprotection procedures. 

Universal methods for coupling of the synthetic building blocks are the Wittig reaction, the Horner-Wadsworth-Emmons reaction, the sulfone coupling by Julia s procedure, the enol ether condensation (Miiller-Cunradi-Pieroh reaction), and the Saucy-Marbet rearrangement. Since in very many cases mixtures... 

The [2,3]-Wittig-Still rearrangement of the phenyl sulfide 51 (n = 0) afforded a mixture of 52 and 53 from a and p approach in 8 92 ratio fScheme 17.9T From the corresponding sulfone 51 (n = 2), use of 2 equiv. n-BuLi selectively yielded 54 in 65% yield with the a stereochemistry, resulting from lithium-ion chelation with the sulfonyl methyl and oxymethyl lithium (51a). The synthesis was continued to attach the side chain, and alkylative macrocyclization gave diol 57 (Scheme 17.9). ... 

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