Multiply metallated organic intermediates: a tris(lithiomethyl)cyclohexane and a hexalithiotrimethylcyclohexanetriolate

Abstract

Lithium di-t-butylbiphenyl (LiDBB) readily cleaves alkyl-sulphur bonds to yield long-lived organolithiums. Using this reagent trilithio species ( 2b) was obtained from tris-phenylthioether ( 1b). The organometallic intermediates ( 2b) and ( 5b) were characterised by their reactions with electrophiles (e.g. D 2O, CO 2, Me 3Si-OTf, Me-OTf) to yield di- and hexasubstituted cyclohexanes ( 3) and ( 6). Prolonged treatment of the trilithoxy tris-phenylthioether ( 1c) with excess LiDBB followed by addition of D 2O and aqueous work-up gave a methyl-deuterated trimethylcyclohexanetriol (D 2.5- 3aα) demonstrating that at least one penta- and one hexalithio intermediate are involved. The structure of the latter intermediate could not be established unambiguously, but the unsymmetrical 1,1-dilithiated species ( 22) is prefered over the symmetrical hexalithio species ( 2c) on the basis of extensive transmetallation observed at the tetra- or pentalithio stage ( as seen in the deuterated phenylthiomethylcyclohexanetriol ( 15) and the absence of compelling evidence for the symmetrical tri(deuteriomethyl)cyclohexanetriol ( 3aβ), as judged from the CH 3, CH 2D, and CHD 2 ratios in the deuterated product (D 2.5- 3aα).