RESUMO
The generation of in situ sp2 -sp3 diboron adducts has revolutionised the synthesis of organoboranes. Organocatalytic diboration reactions have represented a milestone in terms of unpredictable reactivity of these adducts. However, current methodologies have limitations in terms of substrate scope, selectivity and functional group tolerance. Here a new methodology based on the use of simple amines as catalyst is reported. This methodology provides a completely selective transformation overcoming current substrate scope and functional/protecting group limitations. Mechanistic studies have been included in this report.
RESUMO
Lithiation of carbamates followed by borylation provides a powerful method for the homologation of boron reagents. However, when applied to hindered systems (secondary carbamates with tBu-boronic esters) for the construction of two quaternary centers, this methodology fails. Instead, using mixed boranes (tBuBMe2), the synthesis of adjacent quaternary stereogenic centers with full stereocontrol was successful. The process can be repeated two or three times in one pot leading to carbon chains bearing multiple contiguous quaternary stereogenic centers. The boranes were converted into tertiary alcohols or C-tertiary amines using chloramine. The origin of the high selectivity for alkyl over Me group migration was determined computationally.
RESUMO
The catalytic formation of C-C bonds is one of the most useful transformations in organic synthesis. Over the last decade, the use of transition metal nanoparticles (NPs) in catalysis has attracted much interest and their use in C-C bond formation reactions constitutes one of their most important applications, including the Suzuki, Heck, and Sonogashira reactions. This tutorial review highlights recent work in this active area, considering the stabilising agents used to prepare the NPs, the catalytic results and the recycling possibilities.
