Lithium bis(ethylenedioxyboryl)methide and its reactions with carbonyl compounds and with the chlorotriphenyl derivatives of germanium, tin and lead

Article abstract of DOI:10.1016/S0022-328X(00)90155-4

Transesterification of tris(dimethoxyboryl)methane, HC[B(OCH₃)₂]₃, with ethylene glycol yielded tris(ethylenedioxyboryl)methane (I), HC(BO₂C₂H₄)₃ which with methyllithium in THF at -70°C precipitated lithium bis(ethylenedioxyboryl)methide (II), Li⁺ HC(BO₂C₂H₄)₂^-. Reaction of II with Ph₃MCl, where M = Ge, Sn, or Pb, gave Ph₃MCH(BO₂C₂H₄)₂. The analogous 1,3-propanediol ester, Li⁺HC(BO₂C₃H₆)₂^-, yielded Ph₃MCH(BO₂C₃H₆)₂. Treatment of Ph₃SnCH(BO₂C₂H₄)₂ with MeLi followed by Ph₃SnCl gave (Ph₃Sn)₂CHBO₂C₂H₄, showing that one B and one Sn atom are sufficient to stabilize a carbanion. Reaction of II with aldehydes gave high yields of 1-alkene-1-boronic esters, RCHCHBO₂C₂H₄, with unexpectedly high stereoselectivity, 90-100% trans by NMR analysis. Aqueous work-up of these boronic esters yielded the boronic acids, RCHCHB (OH)₂, which crystallized as the pure trans isomers. Ketones react with II in an analogous manner. The reaction with acetophenone was not stereospecific. Functional group compatibility has been demonstrated in condensations of II with 1,3-dichloroacetone, cinnamaldehyde, p-nitrobenzaldehyde, and p-dimethylaminobenzaldehyde. The trans geometry of the major isomer of CH₃CHCHBO₂C₂H₄ was proved by B-butylation with butyllithium followed by rearrangement with iodine and base to form cis-2-heptene, a sequence of known stereochemistry, and analogous structure proofs were carried out with cis-CH₃CHCHBO₂C₂H₄ and trans-C₆H₅CHCHBO₂C₂H₄.