4.5 Synthesis of Heterocycles
Since nitrogen-containing heterocycles are omnipresent in natural products and
bioactive molecules, their synthesis under mild conditions, using efficient and
green methodologies, is an important topic. A novel route towards heterocycles
from alcohols using an acceptorless dehydrogenative coupling (ADC) fits well with
such sustainability demands [96]. Kundu reported the synthesis of
2-alkylaminoquinolines from o-amino-benzyl alcohol, benzyl nitriles and primary
alcohols, catalysed by 3.5 mol% ruthenium pincer complex 57 [97]. This procedure
is a one-pot two-step synthesis, which first step required Ru catalyst, nitrile, oaminobenzyl alcohol and base in dioxane for 0.5 h at 125
C for the formation of the
2-aminoquinoline, followed by the addition of 2 equivalents of primary alcohol for
the borrowing hydrogen-type alkylation of the 2-amino group. The methodology
was demonstrated on six examples, two of which were performed on gram scale;
yields ranged from 45 to 78% (Table 18). Kundu also used a new cobalt pincer
complex 58 bearing an NNN ligand as catalyst for this reaction (Scheme 53)
Scheme 52 Nickel PNP pincer complex-catalysed amidine formation
Table 18 Synthesis of 2-alkylaminoquinolines from o-aminobenzyl alcohol, benzyl nitriles and
primary alcohols catalysed by Ru pincer complex 57
a
a Isolated yields
370
B. Guo et al.
Since nitrogen-containing heterocycles are omnipresent in natural products and
bioactive molecules, their synthesis under mild conditions, using efficient and
green methodologies, is an important topic. A novel route towards heterocycles
from alcohols using an acceptorless dehydrogenative coupling (ADC) fits well with
such sustainability demands [96]. Kundu reported the synthesis of
2-alkylaminoquinolines from o-amino-benzyl alcohol, benzyl nitriles and primary
alcohols, catalysed by 3.5 mol% ruthenium pincer complex 57 [97]. This procedure
is a one-pot two-step synthesis, which first step required Ru catalyst, nitrile, oaminobenzyl alcohol and base in dioxane for 0.5 h at 125
C for the formation of the
2-aminoquinoline, followed by the addition of 2 equivalents of primary alcohol for
the borrowing hydrogen-type alkylation of the 2-amino group. The methodology
was demonstrated on six examples, two of which were performed on gram scale;
yields ranged from 45 to 78% (Table 18). Kundu also used a new cobalt pincer
complex 58 bearing an NNN ligand as catalyst for this reaction (Scheme 53)
Scheme 52 Nickel PNP pincer complex-catalysed amidine formation
Table 18 Synthesis of 2-alkylaminoquinolines from o-aminobenzyl alcohol, benzyl nitriles and
primary alcohols catalysed by Ru pincer complex 57
a
a Isolated yields
370
B. Guo et al.