Reactions of "Cp2Ti=CH2" Sources with Acid Anhydrides and Imides

Article abstract of DOI:10.1021/jo00213a023

The reaction of Cp2H2 (3a) with acid anhydrides gave Cp2Ti(OC(O)R)(OC(R)=CH2) (4) in moderate yields.Reaction of 4 with 3a and anhydrides produced 2O (5) and Cp2Ti(OC(O)R)2 (7), respectively.The enolate 4c (R = Ph) reacted with benzaldehyde to form the dehydrated aldol product chalcone (8).Selected 2,5-pyrrolidinediones upon treatment with 1 equiv of Cp2TiCH2*AlMe2Cl (1) or 3a yielded mixtures of 5-methylene-2-pyrrolidinones and 2,5-dimethylenepyrrolidines while use of 2 equiv of 1 or 3a gave exclusively the dimethylene products, potential "dienamine" precursors of 1,2,5-trisubstituted pyrroles.Regioselective methylene transfer was observed for 3,3-dimethyl-2,5-pyrrolidinediones, giving 3,3-dimethyl-5-methylene-2-pyrrolidinones in high yields.Treatment of 1-(3-butenyl)-3,3-dimethyl-5-methylene-2-pyrrolidinone (12n) (formed from the parent 2,5-pyrrolidinedione and 1) with HCO2H gave the cyclized product 1-aza-4-(formyloxy)-6,8,8-trimethylbicyclo<4.3.0>nonan-9-one (14a) exemplifying a potential method for the synthesis of alkaloid analogues.Reaction of 3,3-dimethyl-2,6-piperidinediones with either 1 or 3a formed mixtures of the single methylene-transfer products 3,3-dimethyl-5-methylene-2-piperidinones and titanium enolates of the starting 2,6-piperidinediones.The enolate (16d) of 3,3-dimethyl-1-(2,6-dimethylphenyl)-2,6-piperidinedione was unreactive toward benzaldehyde, even upon prolonged heating.