ChemInform Abstract: Biphenylenes with Strongly Distorted Trapezoidal Four-Membered Ring.

ChemInform Abstract

In search of bridged biphenylenes for the study of added strain to the four-membered ring the synthesis of (IIIc) is undertaken. But on reacting dibromide (Ia) with thiourea (II) the desired disulfide product (Ib) (very unstable) is accompanied unexpectedly by the sulfide (IIIa) which can be prepared from (Ia) as shown. Oxidation yields the sulfone (IIIb) but neither photolysis (230 nm in triethylphosphite) nor thermolysis (650 °C/10^-3 torr) leads to the hitherto unknown hydrocarbon (IV). Both (IIIa) and (IIIb) are examined by X-ray analysis, UV, 90 and 400 MHz ¹H NMR (barriers of ring inversion 49 and 53 kJ/mol, respectively). Results of MNDO calculations on biphenylene, (IIIa), and (IV) are given.