A general route to 1,2,4-trisubstituted pyrimidines is described in one to three steps from a common key precursor, diazadienium iodide 2. An efficient preliminary [4+2] cyclocondensation reaction between the azabutadiene building block 2 and various iso(thio)cyanates constitutes an original construction of the pyrimidine skeleton. Subsequent structural modifications on the heterocycle allow the elaboration
Improved One-Step Procedure for the Preparation of 1-Substituted and 1,3-Disubstituted Uracils and 2-Thiouracils
作者:Ib Winckelmann、Erik H. Larsen
DOI:10.1055/s-1986-31867
日期:——
A convenient one-pot procedure for the synthesis of 1-substituted and 1,3- disubstituted uracils and 2-thiouracils consists of acylation of ureas, or thioureas with methyl 3,3-dimethoxypropanoate in the presence of a strong base, and acidic work-up. The yields range from 36 to 99%. In all cases, only one regioisomer is isolated.
A facile and simple regioselective synthesis of uracils and their thio analogues has been achieved by cyclocondensation of a common precursor, diazadienium iodide 1, and isothiocyanates 2a,b. The key step in this synthetic process is the preparation of 4-methylsulfanylpyrimidine-2-thiones 3a,b, which after further elaboration gave the expected uracil analogues 4a,b-8a,b.