Enantioselective Synthesis of Siloxyallenes from Alkynoylsilanes by Reduction and a Brook Rearrangement and Their Subsequent Trapping in a [4+2] Cycloaddition
Two flavors of selectivity: An enantioselective Meerwein–Ponndorf–Verley‐type reduction of alkynoylsilanes by a chiral lithium amide followed by a Brookrearrangement and SE2′ electrophilic substitution provides the title compounds in a one‐pot process. In the case of enynoylsilanes, the generated vinylallenes undergo in situ [4+2] cycloaddition to afford highly functionalized polycyclic compounds
两种选择性:通过手性锂酰胺的对映选择性Meerwein-Ponndorf-Verley型还原炔基硅烷,然后进行Brook重排和S E 2'亲电取代,可在一锅法中得到标题化合物。在烯丙基硅烷的情况下,生成的乙烯基亚烷基会进行原位[4 + 2]环加成反应,以提供具有非常规的面部选择性的高度官能化的多环化合物。
Enantioselective Synthesis of α-Silylamines by Meerwein–Ponndorf–Verley-Type Reduction of α-Silylimines by a Chiral Lithium Amide
Meerwein-Ponndorf-Verley-type reduction of N-tosylsilylimines with chiral lithium amide 2 affords alpha-silylamines in high enantioselectivity. Since the enantioselectivity observed was inconsistent with our previously proposed chairlike six-membered transition structure, we performed density functional theory (DFT) calculations on transition states leading to (S)- and (R)-7a and (S)- and (R)-7e using an N-phenylsulfonyl derivatives 12 and 13 as model systems. Results of the calculations showed that the structures are considerably deformed from the chairlike form with steric repulsions between the 1'-methylene group and the imine-carbon substituents playing an important role in the control of the, enantioselectivity.