The initial [2 + 2]-cycloadduct between a chromium aminocarbene and a tethered alkene undergoes a beta-hydrogen elimination very efficiently when triphenylphosphine is added as a ligand. The reaction gives cyclic enamines or homoenamines depending on the substitution on the alkene.
Pd(ii)-catalyzed alkylation of unactivated C(sp3)–H bonds: efficient synthesis of optically active unnatural α-amino acids
作者:Kai Chen、Fang Hu、Shuo-Qing Zhang、Bing-Feng Shi
DOI:10.1039/c3sc51747k
日期:——
A palladium-catalyzedalkylation of primary and secondary C(sp3)–H bonds with alkyl iodides and/or bromides for the synthesis of optically active unnatural α-amino acids (α-AAs) is described. This process is scalable and tolerates a variety of functional groups with complete retention of chirality, providing an efficient new strategy for the synthesis of various unnatural α-amino acid derivatives.
Generation of α-lithio-Se, O-heteroacetals was accomplished by direct deprotonation of O-methoxyethylselenoacetals with lithium 2, 2, 6, 6-tetramethylpiperidide. Alkylation of the α-lithioheteroacetals smoothly proceeded to give the products 6 and 7. Olefinic Se, O-heteroacetals 6c and 6d were cyclized via α-seleno carbenium ions generated by selective C-O bond cleavage with titanium tetrachloride to provide the cyclohexane derivatives 8a and 8b, respectively.