RESUMEN
Alkyl sulfonamides are an important class of bioactive molecules. Historical syntheses have relied on multistep sequences incorporating harsh reaction conditions. Photochemical methods have been limited to hydrosulfamoylation, installing only one substituent across an olefin. Herein, radical/polar crossover (RPC) is used to establish the first multicomponent 1,2-difunctionalization reaction incorporating a sulfonamide moiety and a second reaction partner. This protocol, exemplified on a range of olefins, utilizes various commercial sulfamoyl chlorides and organotrifluoroborates as coupling partners.
RESUMEN
Alkene 1,2-dicarbofunctionalizations are highly sought-after transformations as they enable a rapid increase of molecular complexity in one synthetic step. Traditionally, these conjunctive couplings proceed through the intermediacy of alkylmetal species susceptible to deleterious pathways including ß-hydride elimination and protodemetalation. Herein, an intermolecular 1,2-dicarbofunctionalization using alkyl N-(acyloxy)phthalimide redox-active esters as radical progenitors and organotrifluoroborates as carbon-centered nucleophiles is reported. This redox-neutral, multicomponent reaction is postulated to proceed through photochemical radical/polar crossover to afford a key carbocation species that undergoes subsequent trapping with organoboron nucleophiles to accomplish the carboallylation, carboalkenylation, carboalkynylation, and carboarylation of alkenes with regio- and chemoselective control. The mechanistic intricacies of this difunctionalization were elucidated through Stern-Volmer quenching studies, photochemical quantum yield measurements, and trapping experiments of radical and ionic intermediates.
RESUMEN
The enantioselective syntheses of (-)-coniine, DAB-1, and nectrisine have been developed, utilizing a complementary strategy of enzyme- and transition metal-catalyzed reactions. The initial stereocenter was set with >99% enantioselectivity via an enzyme-catalyzed hydrocyanation reaction. Substrate incompatibilities with the natural enzyme were overcome by tactical utilization of ruthenium-catalyzed olefin metathesis to functionalize an enzyme-derived (R)-allylic fragment. The piperidine and pyrrolidine alkaloid natural products were obtained by a route that leveraged regio- and stereoselective palladium-catalyzed 1,3-substitutive reactions.
RESUMEN
Reactions that directly install nitrogen into C-H bonds of complex molecules are significant because of their potential to change the chemical and biological properties of a given compound. Although selective intramolecular C-H amination reactions are known, achieving high levels of reactivity while maintaining excellent site selectivity and functional-group tolerance remains a challenge for intermolecular C-H amination. Here, we report a manganese perchlorophthalocyanine catalyst [MnIII(ClPc)] for intermolecular benzylic C-H amination of bioactive molecules and natural products that proceeds with unprecedented levels of reactivity and site selectivity. In the presence of a Brønsted or Lewis acid, the [MnIII(ClPc)]-catalysed C-H amination demonstrates unique tolerance for tertiary amine, pyridine and benzimidazole functionalities. Mechanistic studies suggest that C-H amination likely proceeds through an electrophilic metallonitrene intermediate via a stepwise pathway where C-H cleavage is the rate-determining step of the reaction. Collectively, these mechanistic features contrast with previous base-metal-catalysed C-H aminations and provide new opportunities for tunable selectivities.
