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

Novel N,N,N-tridentate beta-diketiminato rare-earthmetal dialkyl complexes LRE(CH2SiMe3)(2) [RE = Y (1a), Gd (1b), Yb (1c), Lu (1d); L = MeC(NDipp)CHC(Me)N(CH2)(2)NC4H8, where Dipp = 2,6-(Pr2C6H3)-Pr-i] have been conveniently synthesized by one step from reactions of the rare-earth-metal trialkyl complexes RE(CH2SiMe3)(3)(THF)(2) (THF = tetrahydrofuran) with a pyrrolidine-functionalized beta-diketiminate HL, 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, {[eta(2)-(4-MePhNCO)(CH2SiMe3)]Y[mu-eta(2):eta(1):eta(1)-(4-MePhNCO)-CC(Me)(NDipp)C(Me)N(CH2)(2)NC4H8]} 2 (7a), with two different amidate units, which underwent an sp(2) C-H bond activation of the beta-diketiminato backbone, followed by the insertion of isocyanate.

Automated summary

Novel N,N,N-tridentate beta-diketiminato rare-earthmetal dialkyl complexes have been synthesized and their catalytic behaviors towards hydroalkoxylation and tandem hydroalkoxylation/cyclohydroamination reactions have been investigated.