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You are using Science Of Synthesis as a Guest. Please login or sign up for a free trial to access the full content. Variation 2: Electrophilic Addition of C2

DOI: 10.1055/sos-SD-037-00384

Inoue, M.; Yamashita, S.Science of Synthesis, (200837598.

An intramolecular silyl-modified Sakurai reaction has been used as a powerful tool for the construction of tetrahydropyrans (Scheme 17).[‌83‌,‌84‌] Direct condensation of carbonyl compounds 92 and silyl ether 93 under the influence of trimethylsilyl trifluoromethanesulfonate produces tetrahydropyran 94 in a single step. The reaction involves the intermolecular acetalization and subsequent intramolecular nucleophilic attack of the allylsilane onto an in situ generated oxonium cation. The similar trimethylsilyl trifluoromethanesulfonate promoted annulation of silanes with aldehydes has been applied to the synthesis of a potential BC ring subunit for antitumor agent bryostatin 1 (Scheme 17).[‌85‌,‌86‌] Reaction of enal 96 with the hydroxy allylsilane 95 generates the desired bicyclic product 97 in a stereoselective manner. The stereochemical outcome is in accord with the expectation that cyclization occurs via a chair-like transition state with two alkyl chains equatorially disposed.

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