By S. V. Babu, S. Danyluk, M. I. Krishnan, M. Tsujimura
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Extra info for Chemical Mechanical Polishing /Fundamentals and Challenges: Symposium Held April 5-7, 1999, San Francisco, California, U.S.A
The chemical instability of the adducts precluded the unequivocal assignment of their absolute configurations. Assignment was therefore based on the assumption that in the presence of 1 equiv. of catalyst, the approach of diene taking place from the less hindered face of the chelated species A (Scheme 25). The exclusive formation of the exo-51 adducts with Dane’s diene contrasts with the predominance of the endo adducts obtained with cyclic dienes (Scheme 25). This increase of the exo selectivity (with respect to the sulfinyl group) observed in reactions with acyclic dienes has also been found for sulfinyl butenolides (see above) and other sulfinyl esters such as acrylates and maleates (see later).
These reactions occur with high levels of endo/exo and p-facial selectivity, with the exo(c) adducts being the major products. The influence of catalysts such us Eu(fod)3 (affording the highest p-facial selectivity but the lowest endo/exo selectivity) and ZnBr2 (inverting the p-facial selectivity in the reaction with cyclopentadiene and thus yielding the exo(t) adduct as the major one) remained identical to that observed for compound 95. More interesting were the results obtained in reactions of 99 with acyclic dienes catalyzed by Eu(fod)3 (–20°C) and TiCl4 (–78°C).
1 :1 mixtures) was increased in the presence of Lewis acids, the best results being obtained in the presence of BF3 · OEt2 (93:7 mixture). Reactions of optically pure sulfinyl enones with acyclic dienes have never been reported, perhaps as a result of the discouraging results obtained from racemic substrates . The reaction of a-phenylsulfinyl a,b-unsaturated ketones with butadiene and 2,3-dimethyl butadiene, under Lewis acid catalysis, yielded the cyclohexadienes resulting from spontaneous elimination of sulfenic acid (precluding any conclusion about the stereoselectivity of the reaction).