A Versatile Synthesis of 1-Benzoheteroepines Containing Group 14, 15, and 16 Heavier Elements via a Common 1, 6-Dilithium Intermediate

Fully unsaturated group 14 (Si, Ge, and Sn), group 15 (P, As, Sb, and Bi) and group 16 (S, Se, and Te) 2-trimethylsilyl-1-benzoheteropines (16a-j), including the first isolated examples of bismepines, have been prepared by reaction of the corresponding electrophilic metal reagents (MX2 or MX4; M=group 14, 15, and 16 heavier elements) with the key 1, 6-dilithium intermediate (9), generated from the common starting compound (Z, Z)-1-bromo-4-(2-bromophenyl)-1-trimethylsily-1, 3-butadiene (14) by treatment with tert-butyllithium. The trimethylsilyl group in 16b-j was readily removed by treatment with tetrabutylammonium fluoride to give the desired C-unsubstituted 1-benzoheteroepines (1b-j). Single crystal X-ray analyses of 1d (P) and 1f (Sb) revealed that the seven-membered rings exist in boat conformations with the heteroatoms at the bows. All obtained C-unsubstituted group 15 and 16 1-benzoheteroepines (1d-j) were thermolabile in solution towards heteroatom extrusion, while heteroepines (16d-j) having the bulky trimethylsilyl group at the 2-position were much more stable than 1d-j. The half-lives of 1d-j estimated from 1H-NMR spectral analysis indicate that the thermal stabilities of 1d-j decrease in the order 1f (Sb)>1d (P)>1e(As)>1g(Bi) in the group 15 heteroepines and 1j (Te) 1h (S) in the group 16 heteroepines.