Studies on 6-[(Dimethylamino)methylene]aminouracils: a Facile One-pot Synthesis of Pyrimido[4,5-d]pyrimidines and Pyrido[2,3-d]pyrimidines.
作者:Ashim J. Thakur、Promod Saikia、Dipak Prajapati、Jagir S. Sandhu
DOI:10.1055/s-2001-16036
日期:——
6-[(Dimethylamino)methylene]amino-1,3-dimethyl uracil 1 undergoes formal [4 + 2] cycloaddition reaction with nonconjugated imines to give pyrimido[4,5-d]pyrimidines 3. When reacted with conjugated imines and α,β-unsaturated nitro compounds cycloaddition also occurs leading to unexpected pyrido[2,3-d]pyrimidines 5 and 9, respectively.
Cyclic amines such as 1,2,3,4-tetrahydroisoquinoline undergo regiodivergent annulation reactions with 4-nitrobutyraldehydes. These redox-neutral transformations enable the asymmetric synthesis of highly substituted polycydic ring systems in just two steps from commercial materials. The utility of this process is illustrated in a rapid synthesis of (-)-protoemetinol. Computational studies provide mechanistic insights and implicate the elimination of acetic acid from an ammonium nitronate intermediate as the rate-determining step.