Diversified reactions of enol diazoacetate in chemical catalysis

Silylated enol diazoacetates, prepared by the selective O-silylation of diazoacetoacetates in the presence of a mild base, are extremely valuable in synthesizing noval heterocyclic compounds. The incorporation of a silyl enol unit in the &agr;-diazoacetate moiety creates a unique molecule that displays multifaceted reactivities under the catalysis of conceptually different catalytic systems.;Upon catalytic dinitrogen extrusion of silylated enol diazoacetate by dirhodium catalysis, the corresponding rhodium bound enol carbene intermediate resembles a metallo-1,3-dipolar species and undergoes a formal dearomatizing [3+3]-cycloaddition with isoquinolinium/pyridinium methylides that furnishes substituted quinolizidines. The development of the catalytic asymmetric variant of this cycloaddition reaction by catalysis with the previously unreported chiral dirhodium carboxylate catalyst-Rh2(S-PTIL)4 has allowed convenient access to highly enantioenriched quinolizidines. Coordination of the Lewis basic methylides to dirhodium(II) prompts the rearrangement of the enol carbene that is bound to dirhodium to produce a donor--acceptor cyclopropene which undergoes a diastereoselective [3+2]-cycloaddition with isoquinolinium/pyridinium methylides. With the overall reaction outcome controlled by the amount of catalyst used, an increase in the mol % of catalyst loading suppresses the [3+2]-cycloaddition pathway.;In a reaction that proceeds under mild conditions with remarkable functional group tolerance, catalytically generated rhodium enol carbene intermediate reacts with nucleophilic silylated ketene imines and produced structurally diverse 3-amino-2-cyclopentenones bearing a quaternary carbon at the 4-position in high efficiency. The key step for the overall transformation emanates from the [3+2]-cycloaddition of silylated ketene imine and rhodium enol carbene with the nucleophilic silylated ketene imine attacking the vinylogous position of rhodium enol carbene.;Under Lewis acid catalysis, silylated enol diazoacetates participates in diastereoselective [3+2]-cycloaddition reactions with azomethine imines to produce highly functionalized beta-methylene-beta-silyloxy-beta-amido-&agr;-diazoacetates. Catalyst-directed selectivity of competitive 1,2-C→C, -O→C and -N→C migrations from the beta-methylene-beta-silyloxy-beta-amido-&agr;-diazoacetates demonstrates that the differential selectivities rely on the control of the stereoelectronic property of the catalytically generated metal carbenes.