Benzyne tethered alkyllithiums

It has been shown that, in the presence of lithium diethylamide at —70 °C, bromoben-zoic acids form arynes which may react with arylacetonitriles to yield, predominantly, 2-cyanobenzoic acids. The reaction of alkyl and aryl isocyanides with benzyne may yield benzamide derivatives, showing their ability to act as charge-reversed equivalents to isocyanates. The generation and cyclization of a benzyne-tethered alkyllithium have been reported, and lead to a convenient synthetic route for 4-substituted indans. ... 

In light of the facile 5-exo-dig carbolithiation reaction of simple acetylenic alkyllithiums, Bailey and Longstaff have studied the analogous 5-exo cyclization of a benzyne-tethered alkyllithium. Regioselectively 4-functionalized indanes 281 have been prepared... 

These authors have extended this reaction to the preparation of 3-substituted benzocy-clobutenes 283 (n = 1) and 5-substituted tetralins 283 (n = 3) from a-(2-fluorophenyl)-tw-iodoalkanes 282. In a similar way as described above, the processes involve generation and cyclization of benzyne-tethered alkyllithiums via 4-exo or 6-exo, though in these cases the yields are significantly lower (Scheme 74)132. 

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