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Chelation-assisted substrate-controlled asymmetric lithiation-allylboration of chiral carbamate 1,2,4-butanetriol acetonide.

ABSTRACT: 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.

SUBMITTER: Mahmood A

PROVIDER: S-EPMC6272734 | biostudies-literature | 2015 May

REPOSITORIES: biostudies-literature

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Chelation-assisted substrate-controlled asymmetric lithiation-allylboration of chiral carbamate 1,2,4-butanetriol acetonide.

Mahmood Adeem A Alkhathlan Hamad Z HZ Parvez Saima S Khan Merajuddin M Shahzad Sohail A SA

Molecules (Basel, Switzerland) 20150528 6

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 ...[more]

PMID: 26029858

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