3.3 α-Alkylation of Aliphatic and Benzylic Nitriles via
Michael Addition on Unsaturated Ketones or Esters
Milstein and co-workers studied the reactivity of a Re complex based on a pyridinecontaining PNP
tBu pincer with nitriles and found novel pathways for the activation
of the CN bond [17]. Based on the aromatisation and dearomatisation of the
pyridine in the ligand backbone, the stoichiometric reaction of nitriles with the
pincer complex 24 resulted in ketimido or enamino adducts, with remarkably low
energy barriers. In addition, these processes are highly reversible (Scheme 24),
opening the way to a lot of interesting reactivities. Taking advantage of these, they
successfully demonstrated the Michael addition of benzyl nitriles to α,β-unsaturated
esters and ketones with moderate to excellent yields (Table 11).
Based on the stoichiometric studies, they proposed the following mechanism:
reaction of 24 with benzyl cyanide leads to the enamido complex I. This complex
reacts as a nucleophile in a Michael reaction on methyl acrylate to form the
Table 10 Olefination of nitriles with alcohols by 19
a
a Isolated yields
b Using 2 mol % catalyst and 4 mol % base
c
Reaction time of 24 h
d Using 5 mol % catalyst 1 and 10 mol % base
344
B. Guo et al.
Michael Addition on Unsaturated Ketones or Esters
Milstein and co-workers studied the reactivity of a Re complex based on a pyridinecontaining PNP
tBu pincer with nitriles and found novel pathways for the activation
of the CN bond [17]. Based on the aromatisation and dearomatisation of the
pyridine in the ligand backbone, the stoichiometric reaction of nitriles with the
pincer complex 24 resulted in ketimido or enamino adducts, with remarkably low
energy barriers. In addition, these processes are highly reversible (Scheme 24),
opening the way to a lot of interesting reactivities. Taking advantage of these, they
successfully demonstrated the Michael addition of benzyl nitriles to α,β-unsaturated
esters and ketones with moderate to excellent yields (Table 11).
Based on the stoichiometric studies, they proposed the following mechanism:
reaction of 24 with benzyl cyanide leads to the enamido complex I. This complex
reacts as a nucleophile in a Michael reaction on methyl acrylate to form the
Table 10 Olefination of nitriles with alcohols by 19
a
a Isolated yields
b Using 2 mol % catalyst and 4 mol % base
c
Reaction time of 24 h
d Using 5 mol % catalyst 1 and 10 mol % base
344
B. Guo et al.