Asymmetric Synthesis and Characterization of Chiral 2,2′‐Diamino‐3,3′‐diethoxycarbonyl‐8,8′‐diphenyl‐1,1′‐biazulene

Abstract

rac‐2,2′‐Diamino‐3,3′‐diethoxycarbonyl‐8,8′‐diphenyl‐1,1′‐biazulene was synthesized from diethyl 2‐aminoazulene‐1,3‐dicarboxylate and was optically resolved into two enantiomers of S‐form and R‐form. The enantioselective oxidative couplings with two chiral amines [(−)‐sparteine and (R)‐(+)‐α‐methylbenzylamine] and ferric chloride catalyst, and the asymmetric couplings with two chiral oxovanadium(IV) complexes of ethyl 2‐amino‐4‐phenylazulene‐1‐carboxylate, easily yielded chiral 2,2′‐diamino‐3,3′‐diethoxycarbonyl‐8,8′‐diphenyl‐1,1′‐biazulene. Therefore, the introduction of two phenyl groups at the 8‐ and 8′‐postions of each azulene ring using phenyl magnesium bromide via an addition–oxidation–decarboxylation mechanism resulted in 1,1′‐biazulene forming a chiral C₂ axis.

Keywords:

• asymmetric couplings with chiral oxovanadium(IV) complexes
• CD
• chiral 1,1′‐biazulene
• enantioselective oxidative couplings

Acknowledgment

This study was financially supported by the National Science Council of the Republic of China (NSC93‐2113‐M‐218‐003). We thank L. S. Chang of National Sun Yat‐Sen University for circular dichroism (CD) measurement.