| Abstract
| - To explore a novel concept for controlling diastereoselectivity, systematic studies on the sense anddegree of diastereotopic groups and face selections in intramolecular [3 + 2] (nitrile oxide andnitrone) and [2 + 2 + 1] (Pauson−Khand) cycloadditions have been conducted. Optically pure methyl(S)-3,4-O-isopropylidene-3,4-dihydroxybutanoate (5) and methyl (S)-2,3-O-isopropylidene-2,3-dihydroxypropanoate (6) were converted to substrate aldehydes (1−4) that bear geminal allyl groupsand four types of controllers with the intention of imparting a stereochemical bias to the allylicgroups and their faces. The controllers involve 1,2-bis(tert-butyldimethylsiloxy), 1,3-bis(tert-butyldimethylsiloxy), 1,2-acetonide, and 1,3-acetonide groups, which are referred to as 1,2-(TBDMSO)2, 1,3-(TBDMSO)2, 1,3-dioxolane, and 1,3-dioxane, respectively. Twelve runs of cycloaddition reactions as combinations between the three types of reactions and the four types ofsubstrates were performed to provide bicyclo[4.3.0] or -[3.3.0] adducts of synthetic importance inwhich isoxazolidine, isoxazoline, or cyclopentenone segments were fused. For every case, high levelsof diastereoselectivity have been achieved: >99% (in eight cases), 82%, and 76% for thediscrimination of diastereotopic groups and 68→99% for the discrimination of diastereotopic faces.On the basis of the absolute structures of the cycloadducts, plausible stereochemical models areproposed.
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