RESUMEN
We report a computational study of the transfer of silylium from phosphine to heteroatom containing Lewis bases including ethers, phosphines, and amines. The relative free energies of these compounds are compared to develop a thermodynamic scale of stabilities that can help to interpret the chemoselectivity observed with complex natural products and biomass-derived sugars. Both the choice of silane and the phosphine Lewis base impact the thermodynamics of this transfer.
RESUMEN
A diastereoselective, gold-catalyzed cascading cycloisomerization of alkylidene cyclopropane bearing 1,5-enynes that terminates in a cyclo-addition of aldehydes has been developed. This diastereoselective reaction provides convergent access to novel polycyclic molecular structures (18 examples), and tolerates a diverse scope of aldehydes. Mechanistic studies reveal that the catalytic cycle rests at a digold off-cycle intermediate, one of which was isolated.
RESUMEN
In situ generated benzyne reacts at room temperature with (triphos)Pt-CH3+ to form a five-coordinate π-complex (2) that is isolable and stable in solution. Thermolysis of 2 at 60 °C generates (triphos)Pt(o-tolyl)+ (3), which is the product of formal migratory insertion of CH3- onto the coordinated benzyne. The reaction of 2 with the acid Ph2NH2+ yields toluene at room temperature over the course of 8 h, while the same reaction with 3 only proceeds to 40% conversion over 2 days. These data indicate that the protonolysis of 2 does not proceed by CH3 migration onto benzyne to form 3 followed by protodemetalation. Instead, the data suggest either that protonation of 2 is first and is followed by H migration to yield a PtIVPh(Me) dication or that this latter species is generated by direct protonolysis of coordinated benzyne prior to reductive elimination of toluene.