Der nachweis der zwischenstufe bei nucleophilen aromatischen substitutionen mit eliminierung; zur struktur der arine

Abstract

Lithium piperidide in ether at 20° is 27 times more efficient in the formation of benzyne from fluorobenzene, and 70 times more efficient with chlorobenzene than is phenyllithium. On the other hand, as competition experiments reveal, benzyme adds phenyllithium 4·4 times as readily as lithium piperidide. This discrepancy between rate of benzyme formation and rate of addition establishes the presence of a selective intermediate. The nature of the halogen in the aryl halide does not influence the product composition. Therefore, the intermediate is regarded as halogen free. In the same system, phenyllithium and lithium piperidide in ether, 1,2-naphthyne and 9,10-phenanthryne show higher competition constants of 5·8 and 12·8 respectively than benzyme. The increasing selectivity of the arynes is the result of an increasing bond energy which stems from a decreasing bond distance.