Macrocycle Formation by Cooperative Selection at a Double-Sited Frustrated Lewis Pair

Hydroboration of the 4,5-bis(allyl,mesityl)phosphanyl xanthene derivative 2 with Piers’ borane [HB(C6F5)2] gave the bis-P/B frustrated Lewis pair 3. In this situation, the two symmetry-equivalent P/B FLP units featured markedly different reaction modes. With resorcinol, they formed the 20-membered macrocycle 11 by a sequence of −OH deprotonation/borane-induced tautomerization. With aryl acetylenes, the 18-membered macrocyclic products 15 (three examples) were formed in a unique sequence of carbon–carbon coupling reactions.