Sulfones diene protection

Regio- and stereoselective dihydroxylation of dienes functionalized at the allylic position with a benzene sulfone group has been reported42. Osmylation of dienic sulfones 33, a potential key synthon for forskolin, occurred exclusively on the A6-7 double bound and preferentially from the a-face of the traws-fused bicyclic molecule, presumably due to a combination of steric and electronic factors (equation 25). While the reaction of diene sulfones proceeded sluggishly under catalytic conditions, treatment of 33a with a stoichiometric amount of OSO4 resulted in quantitative yield of diastereomeric diols 34a and 35 in a 9 1 ratio, respectively. Protecting the hydroxy group of the dienol as its t-butyldimethylsilyl ether (33b) affords diol 34b exclusively. 

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. 

Following this historical precedent, a sulfone was readily appended onto the diene system of 37, affording 38 in 91 % yield (Scheme 7). One should note that in this transformation both isomers obtained from the prior Wittig olefination were employed, resulting in the mixture of stereoisomers at C-9 in 38. Based on the assumption that eventual thermal extrusion of SO2 from either diastereomer would provide the requisite trans-substituted olefin in the diene desired for Diels—Alder reaction, this lack of selectivity was not deemed problematic. However, the pressing issue at this juncture remained the generation of the quinone. Fortunately, with the diene now protected, oxidative demethylation smoothly furnished 39 in 79 % yield with concomitant TBS deprotection. 

Allyl p-tolyl sulfone and tetramethylammonium chloride in methanol cooled to 5°, then electrolyzed with a Hg-cathode and water as anolyte at 18-24 V and 1 amp. until after 30-35 min. vigorous Hg-evolution indicates completion of the reaction p-toluenesulfinic acid (Y 80%) and propylene (Y 75%). F. e. s. L. Horner and H. Neumann, B. 98, 1715 (1965) also selective removal of protective groups from peptides s. B. 98, 3462 (1965) with tetramethylammonium tosylate, ring closures by intramolecular electrolytic reduction of activated dienes s. J. D. Anderson and M. M. Baizer, Tetrah. Let. 1966, 511. 

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