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)
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-TextKeywords:
lithiation; borylation; allylation; chelation
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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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