标题：Chelation-Assisted Substrate-Controlled Asymmetric Lithiation-Allylboration of Chiral Carbamate 1,2,4-Butanetriol Acetonide
作者：Mahmood, Adeem; Alkhathlan, Hamad Z.; Parvez, Saima; Khan, Merajuddin; Shahzad, Sohail A.
作者机构：[Mahmood, Adeem; Alkhathlan, Hamad Z.; Khan, Merajuddin] King Saud Univ, Dept Chem, Coll Sci, Riyadh 11451, Saudi Arabia.; [Mahmood, Adeem; Shahzad, 更多
通讯作者地址：[Mahmood, A]King Saud Univ, Dept Chem, Coll Sci, Riyadh 11451, Saudi Arabia.
关键词：lithiation; borylation; allylation; chelation
摘要：The lithiation of 2-(2,2-dimethyl-1,3-dioxolan-4-yl)ethyl diisopropylcarbamate (1) is achieved freely by sec-butyllithium in diethylether with high lk-diastereoselectivity: the bicyclic chelate complexes 3a and 3b are reacted with electrophiles to form optically active precursors 4a and 4b with >95% diastereoselectivity. In addition, tertiary diamines can undergo an external complexation in contest with the internal oxygen ligand, leading to improved stereoselectivities. The further reactions of lithiated carbamates with trans alkenyl-9-BBN derivatives after 1,2 metallate rearrangements, gave the key intermediate -substituted allylic boranes 7. Subsequent allylboration of aldehydes gave (Z)-anti-homoallylic alcohols 8 in good yield and excellent d.r.