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Molecules 2015, 20(6), 9890-9905; doi:10.3390/molecules20069890

Chelation-Assisted Substrate-Controlled Asymmetric Lithiation-Allylboration of Chiral Carbamate 1,2,4-Butanetriol Acetonide

1
Department of Chemistry, College of Science, King Saud University, Riyadh 11451, Saudi Arabia
2
Department of Chemistry, COMSATS Institute of Information Technology, Abbottabad 22060, Pakistan
3
School of Medicine, Shandong University, Jinan 250012, China
*
Authors to whom correspondence should be addressed.
Academic Editor: Jean Jacques Vanden Eynde
Received: 5 April 2015 / Revised: 19 May 2015 / Accepted: 20 May 2015 / Published: 28 May 2015
(This article belongs to the Section Organic Synthesis)
View Full-Text   |   Download PDF [807 KB, uploaded 28 May 2015]   |  

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 α-substituted allylic boranes 7. Subsequent allylboration of aldehydes gave (Z)-anti-homoallylic alcohols 8 in good yield and excellent d.r. View Full-Text
Keywords: lithiation; borylation; allylation; chelation lithiation; borylation; allylation; chelation
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Mahmood, A.; Alkhathlan, H.Z.; Parvez, S.; Khan, M.; Shahzad, S.A. Chelation-Assisted Substrate-Controlled Asymmetric Lithiation-Allylboration of Chiral Carbamate 1,2,4-Butanetriol Acetonide. Molecules 2015, 20, 9890-9905.

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