Organomolybdenum and Organotungsten Reagents, V[1]. – On the Additive, Reductive Carbonyl Dimerization (ARCD Reaction)
Reagents of the type R4(PrO)4(μ‐PrO)2W2 (3; R = Me, Et, Pr, Bu, sBu, iBu, Hex, Me3SiCH2, Ph) prepared in situ by the action of organolithium or Grignard compounds on (PrO)4(μ‐PrO)2‐W2Cl4 (2), react with aromatic aldehydes or ketones and with the α,β‐unsaturated ketone benzylidene acetone in a novel reaction, called the ARCD reaction, to give products 4 of the type RRRC—CRRR with mostly good yields. In the case of benzylidene acetone and furfural besides the ARCD products the rearranged products 27 and 29 are formed. With the reagent Ph4(PrO)4(μ‐PrO)2W2 (3b) ARCD reactions are also possible in moderate yields with aliphatic aldehydes and ketones. The more closely investigated reagent Me4(PrO)4(μ‐PrO)2W2 (3a; decomposition at about — 45C) tolerates the aromatic bound functional groups Cl, F, OH, OMe, and NMe2 in the substrates, but not the NO2 and CO2Et substituents. It reacts with PhCOX (X = OEt, Cl, OCOPh) via acetophenone to give PhCMe2—CMe2Ph. — For the ARCD reactions a radical mechanism (Scheme 7) is postulated.