Nitrogen nucleophiles, reactions with aryne

Additionally, CO2 has been found to take part in a three-component coupling with arynes and imines, leading to six-membered heterocycles such as benzoxazi-nones 49 (Scheme 12.17) [41]. In contrast to the previous example (Equation 12.27), the imines act as nucleophiles. The use of imines with either steric congestion or decreased nitrogen nucleophilicity significantly slowed the reaction. 

The reactive zwitterions arising from the nucleophilic attack of imines 479 on the benzyne generated in situ from 2-(trimethylsilyl)phenyl triflate 478 proved to be an appropriate molecular scaffold for the capture of CO2 with sufficient electrophilicity to yield 2-aryl-3,l-benzoxazin+-ones 480 (Equation 53). Both substituents of the C=N bond affected the course of the reaction considerably the best yields were achieved by using imines with electron-rich or neutral aryl groups on the carbon, and benzyl or nonbranched chain alkyl substituents on the nitrogen atom. With substituted derivatives of 478, the unsymmetrically substituted arynes led to regioisomeric products <2006JA9308>. 

When 88-1 was treated with phenyl- or methyllithium, no compound of type 90 containing pentacoordinated nitrogen could be obtained. The isolated products, however, could reasonably be attributed to a dehydrobenzene reaction sequence initiated by nucleophilic attack at a hydrogen atom ortho to the ammonium centerI07>. Elimination of triarylamine108> from 91, here in the form of an aryl-carbazole, led to the substituted aryne 92, which added the nucleophiles present to give 93a, 94a and, after hydrolysis, 93b, 94b, respectively. 

---