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 pi) a nd group 16 (S, Sc, and Te) 2-trimethylsilyl-1-benzoheteroepines (16a-j), i ncluding the first isolated examples of bismepines, have been prepared by r eaction of the corresponding electrophilic metal reagents (MX2 or MX4; M-gr oup 14, 15, and 16 heavier elements) with the key 1,6-dilithium intermediat e (9), generated from the common starting compound (Z,Z)-1-bromo-4-(2-bromo phenyl)-1-trimethylsilyl-1,3-butadiene (14) by treatment with tert-butyllit hium. The trimethylsilyl group in 16b-j was readily removed by treatment wi th tetrabutylammonium fluoride to give the desired C-unsubstituted 1-benzoh eteroepines (1b-j). Single crystal X-ray analyses of Id (P) and If(Sb) reve aled that the seven-membered rings exist in boat conformations with the het eroatoms at the bows. All obtained C-unsubstituted group 15 and 16 1-benzoh eteroepines (1d-j) were thermolabile in solution towards heteroatom extrusi on, 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 estimat ed from H-1-NMR spectral analysis indicate that the thermal stabilities of 1d-j decrease in the order If(Sb)>1d (P)>1e (As)>1g (Ei) in the group 15 he teroepines and Ij (Te)>1i (Se)>1h (5) in the group 16 heteroepines.