Diastereoselective acylation of 3,4-dihydro-3-methyl-2H-[1,4]benzoxazines with 2-phenoxy carbonyl chlorides

Add time:09/06/2019    Source:sciencedirect.com

In the search for novel efficient chiral resolving agents, we have studied the diastereoselective acylation of 3,4-dihydro-3-methyl-2H-[1,4]benzoxazine and 7,8-difluoro-3,4-dihydro-3-methyl-2H-[1,4]benzoxazine with acyl chlorides of 2-phenoxy carboxylic acids (2-phenoxypropionic, 2-phenoxyisovaleric, and 2-phenoxy-3-phenylpropionic) in toluene and dichloromethane at different temperatures. HPLC analysis of the acylation products showed the predominant formation of (R∗,S∗)-diastereoisomeric amides in all cases. It was found that acylation with the studied acyl chlorides was highly stereoselective; 2-phenoxyisovaleryl chloride demonstrated the highest stereoselectivity (selectivity factor s up to 499). A model for the diastereoisomeric transition states in the interaction between racemic amine and acyl chloride is proposed.

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