Unique Steric Effect of Geminal Bis(silane) To Control the High Exo-selectivity in Intermolecular Diels-Alder
Zengjin Liu1, Xinglong Lin1, Na Yang2
1Key Laboratory of Drug Targeting and Drug Delivery System, Ministry of Education, Department of Medicinal Chemistry, West China School of Pharmacy, Sichuan University , Chengdu 610041, P. R. China.
Abstract:
The unique steric effect of geminal bis(silane) [(R3Si)2CH] allows an exo-selective intermolecular Diels-Alder reaction of geminal bis(silyl) dienes with α,β-unsaturated carbonyl compounds. The approach shows good generality to form ortho-trans cyclohexenes in good yields with high exo-selectivity and high enantioselectivity in some asymmetric cases. The excellent exo-stereocontrol aptitude of (R3Si)2CH group is highlighted by comparing with R3SiCH2 and R3Si groups, which leads to endo-selectivity predominantly. The conformational analysis of dienes suggests that (R3Si)2CH group effectively shields both sides of the diene moiety, ensuring the desired exo-selectivity. Moreover, the geminal bis(silane) can be further functionalized to transform the resulting ortho-trans cycloadducts into useful synthons, which makes the approach hold great potential for organic synthesis.
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