Thienopyrimidines, formation

Surprisingly, only one example of the synthesis of thieno[3,4-,7 pyrimidines has been described starting from a pyrimidine ring. In CHEC-II(1996) <1996CHEC-II(7)229>, substituted 5-cyanouracils, upon reaction with elemental sulfur, led to the formation of compounds in this class. Now the use of a 5-cyanopyrimidino-2-thione 419 under similar conditions (Equation 156) leads to the thienopyrimidine 420 <1997HC0151>. 

Condensation of 3-acylamino-2-acylthiophenes 92 (R = COR) with ammonium formate gave the corresponding thienopyrimidines 93 (R, R = H or Me) [74CR(C)1513 76BSF151]. The substituted methyl derivatives of 93 (R = XCH2) were prepared by the action of nucleophilic reagents on l,2,3-triazolo[3,4-a]thieno[3,2-d]pyrimidines 94 (80JHC1771). 

Treatment of aminoisothiazolopyrimidine 136 with chloroacetone gave an unexpected transformation. A thienopyrimidine formed, apparently, through the intermediate opening of the isothiazole ring and the formation of the corresponding nitrile (1988JCR(S)46). 

If the nitrogen atom at position 2 bears a substituent, alkylation proceeds at the nitrogen atom in position 4 of the thienopyrimidine system, as exemplified (1988DOK1135, 1989KGS413) by the formation of thiazolothienopyrimidinium salts 185 from S-allyl derivatives 186. 

Thiazolo[3,2-a]tiiieno[2 aiid wOlpyrimidlnes [C3NS-C4S-C4N2].—An attempt to prepare thiazolo[3,2-fl]thieno[3,2-t/]pyrimidines containing basic side-chains by the reaction of a 5-allyl-6-mercapto-thienopyrimidine with bromine followed by base led to the formation of the 2-methyl compound (114). > Subsequent... 

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