Stereodivergent SN2@P Reactions of Borane Oxazaphospholidines: Experimental and Theoretical Studies

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• 作者：Hester Zijlstra ; Thierry Le贸n ; Abel de C贸zar ; C茅lia Fonseca Guerra ; Daniel Byrom ; Antoni Riera ; Xavier Verdaguer ; F. Matthias Bickelhaupt
• 刊名：The Journal of the American Chemical Society
• 出版年：2013
• 出版时间：March 20, 2013
• 年：2013
• 卷：135
• 期：11
• 页码：4483-4491
• 全文大小：545K
• 年卷期：v.135,no.11(March 20, 2013)
• ISSN：1520-5126

文摘

The stereodivergent ring-opening of 2-phenyl oxazaphospholidines with alkyl lithium reagents is reported. N-H oxazaphospholidines derived from both (+)-cis-1-amino-2-indanol and (鈭?-norephedrine provide inversion products in a highly stereoselective process. In contrast, N-Me oxazaphospholidines yield ring-opening products with retention of configuration at the P center, as previously reported by Jug茅 and co-workers. As a result, from a single amino alcohol auxiliary, both enantiomers of key P-stereogenic intermediates could be synthesized. Theoretical studies of ring-opening with model oxazaphospholidines at the DFT level have elucidated the streochemical course of this process. N-H substrates react in a single step via preferential backside S_N2@P substitution with inversion at phosphorus. N-methylated substrates react preferentially via a two-step frontside S_N2@P, yielding a ring-opened product in which the nucleophilic methyl binds to P with retention of configuration. DFT calculations have shown that the BH₃ unit is a potent directing group to which the methyl lithium reagent coordinates via Li in all the reactions studied.