A-heterofunctionalisation

Enantioselective Nickel-Catalysed a-Heterofunctionalisation, and a-Arylation/Alkylation Reactions of Carbonyl Compounds... 

Heterofunctionalisation of carbonyl compounds in the a-position has become an important facet of oiganocatalytic enamine-mediated reactions. In 2005, the Jorgensen group described asymmetric a-sulfenylation of aliphatic aldehydes using TMS-protected prolinol catalysts. The best sulfenylating agent was M-benzylsulfanyl-1,2,4-triazole. Other catalysts, such as proline, prolinol, prolinamide or other secondary amide were less effective. The catalyst with bulkier aromatic groups (C2a) afforded the most enantioselective reaction (Scheme 8.39). 

The sixth chapter of the book was devoted to advances in enantioselective nickel-catalysed a-functionalisation, and to a-alkylation/arylation reactions of carbonyl compounds. A prochiral carbonyl compound can be activated toward electrophilic substitution via the formation of an enol or enolate intermediate, generating a tertiary or quaternary centre at the a-carbon. The use of a non-carbon electrophile leads to heterofunctionalised products, while that of carbon electrophiles affords a-arylated/alkylated carbonyl compounds, and the generation of a new stereogenic centre in these reactions... 

---