Homologation Strategy for the Generation of 1-Chloroalkyl Radicals from Organoboranes.

The generation of 1-bromo and 1-chloroalkyl radicals from organoboranes has been investigated. The direct approach involving the hydroboration of halogenated alkenes is impeded by partial dehalogenation taking place during the hydroboration process. An indirect method involving the generation of B-(1-chloroalkyl)catecholborane by homologation of B-alkylcatecholborane with dichloromethyllithium was developed.

Modular Synthesis of Highly Substituted Pyridines via Enolate α-Alkenylation.

A novel methodology for the synthesis of highly substituted pyridines based on the palladium-catalyzed enolate α-alkenylation of ketones is presented; the formation of aromatic compounds is a new direction for this catalytic C-C bond forming reaction. In the key step, a protected β-haloalkenylaldehyde participates in α-alkenylation with a ketone to afford a 1,5-dicarbonyl surrogate, which then undergoes cyclization/double elimination to the corresponding pyridine product, all in one pot. The β-haloalkenylaldehyde starting materials can be obtained from the corresponding methylene ketone via Vilsmeier haloformylation.

Repairing the thiol-ene coupling reaction.

Thiol-ene coupling (TEC) reactions emerged as one of the most useful processes for coupling different molecular units under reaction mild conditions. However, TEC reactions involving weak CH bonds (allylic and benzylic fragments) are difficult to run and often low yielding. Mechanistic studies demonstrate that hydrogen-atom transfer processes at allylic and benzylic positions are responsible for the lack of efficiency of the radical-chain process.