HETERO PI-SYSTEMS .18. HIGHLY SUBSTITUTED 2,4-DI-TERT-BUTYL-1-BORACYCLOHEXADIENES

Hetero π‐Systems, la. ‐ Highly Substituted 2,4‐Di‐tert‐butyl‐l‐boracyclohexadienes Boracyclohexadiees 14 and 16 with three bulky groups should be ideal starting materials for the preparation of kinetically stabilized borabenzene derivatives. They are formed by substitution reactions of anion 11, which itself is derived from 2,4‐di‐tert‐1‐methoxy‐1‐bora‐2,5‐cyclohexadiene (10) by lithiation. Reaction of lithium compound 11 with ferrous chloride provides the sandwich‐type complex 12. As shown by X‐ray structure analysis, 12 has C2 symmetry with the boron atoms in a syn arrangement in staggered conformation, an unusal feature for borabenzene complexes. Exchange of the methoxy group in the trimethylsilylated substance 16 leads to compounds 18a, 18b, 18c, 18d. Pyrolyses of the various precursors are described. Copyright © 1990 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim