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Chapter 2
Synthesis of substituted pyrimidines via Wittig
2.3 Various synthetic approaches for highly substituted
pyrimidines
A brief literature review on the new synthetic strategies for pyrimidine
derivatives is presented as follows.
In recent years, several interesting Pinner-like approaches have been
developed: Karpov and Muller have been reported the employment of alkynones (βketo
aldehydes’ synthetic equivalents) in a three-component one-pot pyrimidine
synthesis (Figure-15). 35 The coupling of acid chlorides (1) with terminal alkynes (2)
under modified Sonogashira conditions (Et 3 N used in stoichiometric amount)
followed by the addition of aminium or guanidinium salts (4) in the presence of
sodium carbonate gave the 2,4-disubstituted or 2,4,6-trisubstituted pyrimidines (5).
Figure-15
Kiselyov 36 was reported an efficient one-pot approach for the synthesis of
2,4,5,6-tetrasubstituted pyrimidines (Figure-16). Reaction of alkyl- or
benzylphosphonates with aryl nitriles formed unstable aza-Wittig species which were
converted into α,β-unsaturated imines by reaction with aromatic aldehydes. The latter
intermediates were converted into the desired pyrimidine derivatives after
nucleophilic attack by a bidentate nuclophile, usually guanidine or amidine.
Figure-16
Mohammad Movassaghi et al. 37 has described a procedure for the synthesis of
pyrimidine derivatives. It was applicable to a wide range of secondary amides and
nitriles using 2-chloropyridine as a base additive in the presence of Tf 2 O (Figure-17).
Figure-17
Department of Chemistry, Saurashtra university, Rajkot-360005 50