ORGANOMOLYBDENUM AND ORGANOTUNGSTEN REAGE NTS .5. ON THE ADDITIVE, REDUCTIVE CARBONYL DIMERIZATION (ARCD REACTION)

Reagents of the type R4(PrO)4(mu-PrO)2W2 (3; R = Me, Et, Pr, Bu, sBu, iBu, Hex, Me3SiCH2, Ph) prepared in situ by the action of organolithiu m or Grignard compounds on (PrO)4(mu-PrO)2-W2Cl4 (2), react with aroma tic aldehydes or ketones and with the alpha,beta-unsaturated ketone be nzylidene acetone in a novel reaction, called the ARCD reaction, to gi ve products 4 of the type RR'R''C-CRR'R'' 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(Pr O)4(mu-PrO)2W2 (3 b) ARCD reactions are also possible in moderate yiel ds with aliphatic aldehydes and ketones. The more closely investigated reagent Me4(PrO)4(mu-PrO)2W2 (3a; decomposition at about -45-degrees- C) tolerates the aromatic bound functional groups Cl, F, OH, OMe, and NMe2 in the substrates, but not the NO2 and CO2Et substituents. It rea cts with PhCOX (X = OEt, Cl, OCOPh), via acetophenone to give PhCMe2-C Me2Ph. - For the ARCD reactions a radical mechanism (Scheme 7) is post ulated.