title: 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 α-substituted allylic boranes 7. Subsequent allylboration of aldehydes gave (Z)-anti-homoallylic alcohols 8 in good yield and excellent d.r.
authors.affiliation: Department of Chemistry, College of Science, King Saud University, Riyadh 11451, Saudi Arabia. dr.adeem@hotmail.com.|Department of Chemistry, COMSATS Institute of Information Technology, Abbottabad 22060, Pakistan. dr.adeem@hotmail.com.
authors.forename: Adeem
authors.initials: A
authors.lastname: Mahmood
authors.affiliation: Department of Chemistry, College of Science, King Saud University, Riyadh 11451, Saudi Arabia. khathlan@ksu.edu.sa.
authors.forename: Hamad Z
authors.initials: HZ
authors.lastname: Alkhathlan
authors.affiliation: School of Medicine, Shandong University, Jinan 250012, China. daring_saima@hotmail.com.
authors.forename: Saima
authors.initials: S
authors.lastname: Parvez
authors.affiliation: Department of Chemistry, College of Science, King Saud University, Riyadh 11451, Saudi Arabia. mdk.chem@gmail.com.
authors.forename: Merajuddin
authors.initials: M
authors.lastname: Khan
authors.affiliation: Department of Chemistry, COMSATS Institute of Information Technology, Abbottabad 22060, Pakistan. sohail_chem@yahoo.com.
authors.forename: Sohail A
authors.initials: SA
authors.lastname: Shahzad
mesh_terms: D001880:Boranes / Q000138:chemical synthesis*; D000440:Butanols / Q000737:chemistry*; D002219:Carbamates / Q000737:chemistry*; D002614:Chelating Agents / Q000737:chemistry; D004987:Ethers; D008024:Ligands; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry; D020005:Propanols / Q000138:chemical synthesis*; D013237:Stereoisomerism
chemical_list: D001880:Boranes; D000440:Butanols; D002219:Carbamates; D002614:Chelating Agents; D004987:Ethers; D008024:Ligands; D009942:Organometallic Compounds; D020005:Propanols; C046771:butyllithium; D010100:Oxygen
keywords: allylation; borylation; chelation; lithiation