SITE-SELECTIVE HYDROGEN METAL EXCHANGE - COMPETITION AND COOPERATION BETWEEN SUPERBASES AND NEIGHBORING GROUPS

The appropriate choice of a metalating reagent is the key to the optio nal deprotonation of benzylamine derivatives at a position adjacent to the substituent or the nitrogen bearing side chain or even at the ben zylic alpha-position of the latter. Subsequent reaction with suitable electrophiles followed by cyclization affords heterocyclic products su ch as isoquinolines and isoindolones. - Immediately when generated, so me organometallic intermediates can undergo a rapid second hydrogen/me tal exchange process. However, dimetalation is only kinetically, not t hermodynamically favored as a careful investigation of typical cases h as revealed. Moreover, it can be avoided if the donor capacity of the solvent or the polarity of the metalating reagent is increased - Allyl ic organopotassium compounds exhibit intriguing stereopreferences. Thi s pecularity has been exploited in a number of very simple sesquiterpe ne syntheses.