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[摘要]:The Prins cyclization of syn-beta-hydroxy allylsilanes and aldehydes gives cis-2,6-disubstituted 4-alkylidenetetrahydropyrans as sole products in excellent yields regardless of the aldehyde (R '') or syn-beta droxy allylsilane substituent (R') used. By reversing the R '' and R' groups, complementary exocyclic stereocontrol can be achieved. When the anti-beta-hydroxy allylsilanes are used, the Prins cyclization gives predominantly cis-2,6-disubstituted 4-alkylidenetetrahydropyrans, now with the opposite olefin geometry in excellent yield. The proposed reaction mechanism and the observed stereoselectivity for these processes are supported by DFT calculations. |
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