Rare-Earth-Metal-Complex-Catalyzed Hydroalkoxylation and Tandem Hydroalkoxylation/Cyclohydroamination of Isocyanates: Synthesis of Carbamates and Oxazolidinones.

Novel N,N,N-tridentate β-diketiminato rare-earth-metal dialkyl complexes L RE(CH 2 SiMe 3 ) 2 [RE = Y ( 1a ), Gd ( 1b ), Yb ( 1c ), Lu ( 1d ); L = MeC(NDipp)CHC(Me)N(CH 2 ) 2 NC 4 H 8 , where Dipp = 2,6- i Pr 2 C 6 H 3 ] have been conveniently synthesized by one step from reactions of the rare-earth-metal trialkyl complexes RE(CH 2 SiMe 3 ) 3 (THF) 2 (THF = tetrahydrofuran) with a pyrrolidine-functionalized β-diketiminate H L , and their catalytic behaviors toward hydroalkoxylation and tandem hydroalkoxylation/cyclohydroamination of isocyanates have been described. These rare-earth-metal catalysts exhibited high efficiency in the hydroalkoxylation of isocyanates, providing a variety of N -alkyl and N -aryl carbamate derivatives under mild reaction conditions with a rather low catalyst loading (0.04 mol %). More significantly, they can promote a tandem hydroalkoxylation/cyclohydroamination reaction between terminal and internal propargylic alcohols with substituted arylisocyanates, leading to the efficient synthesis of methylene and ( Z )-selective arylidene oxazolidinones in good-to-high yields via consecutive C-O and C-N bond formation. The stoichiometric reaction of 1a with p -tolylisocyanate generated an unusual dinuclear yttrium complex, {[η 2 -(4-MePhNCO)(CH 2 SiMe 3 )]Y[μ-η 2 :η 1 :η 1 -(4-MePhNCO)CC(Me)(NDipp)C(Me)N(CH 2 ) 2 NC 4 H 8 ]} 2 ( 7a ), with two different amidate units, which underwent an sp 2 C-H bond activation of the β-diketiminato backbone, followed by the insertion of isocyanate.