Electrophilic heterocyclization of 6-alken(yn)ylsulfanyl-pyrazolo[3,4-d]pyrimidin-4(5H)-ones

Synthesis of new imidazo[1,2-a]pyrazolo[4,3-e]pyrimidin-4(6H)-one derivatives by iodocyclization of 6-alkenyl(alkynyl)-aminopyrazolo[3,4-d]pyrimidin-4(5H)-ones

“…Compound VIIIb characteristically showed in the 1 H NMR spectrum a large difference in the positions of signals from olefinic protons, one of which was displaced strongly upfield (δ 3.50 ppm) due to deshielding effect of the benzene ring on N 1 oriented orthogonally to the exocyclic double bond plane. Analogous shifts of olefinic proton signals were observed by us previously [1], and angu- lar structure of the corresponding cyclization product was proved by X-ray analysis. The positions of the carbonyl absorption band in the IR spectrum and of the C 4 signal in the 13 C NMR spectrum were almost similar.…”

“…We previously showed [1,2] that cyclization of 6-allyl(prop-2-yn-1-yl)sulfanylpyrazolo [3,4-d]pyrimidin-4(5H)-ones by the action of iodine or sulfuric acid provides a convenient method for the synthesis of 4H-pyrazolo [4,3-e]thiazolo [3,2-a]pyrimidin-4-one derivatives. Taking into account pronounced pharmacological effect of their bioisosters (in particular, imidazo [1,2-a]pyrazolo [4,3-e]pyrimidines are efficient phosphodiesterase inhibitors [3][4][5][6]), it seemed important to develop new preparatively simple procedures for the synthesis of such compounds.…”

Cyclofunctionalization of 6-alkenylsulfanylpyrazolo[3,4-d]-pyrimidin-4(5H)-ones with arenesulfenyl chlorides

“…The regioselectivity of the addition of PhSCl at the allyl fragment of I was confirmed by subsequent intramolecular cyclization of compound IV by the action of sodium acetate in dimethyl sulfoxide, which afforded linearly fused pyrazolopyrimidothiazine V. In this case, the cyclization involved the N 5 atom of the pyrazolopyrimidine system, as clearly followed from the presence of carbonyl absorption band at 1715 cm -1 in the IR spectrum of V [6,8].…”

“…Judging by the position of the carbonyl absorption band in the IR spectrum (1700 cm -1 ), compound XIІ is a linearly fused heterocyclic system [6,8].…”

Fused pyrimidine systems: XVI. Electrophilic intramolecular cyclization of 2-(alkenylsulfanyl)pteridin-4(3H)-ones

“…For the sysnthesis of partially hydrogenated thiazolo(thiazino)pteridines, also of those containing functional substituents, a promising reaction seems to be the electrophilic intramolecular cyclization of 2-(alkenylsulfanyl)pteridines. This approach was formerly successfully applied to the preparation of related polyheterocyclic systems: thiazolo(thiazino)thienopyrimidines [8,9], thiazolo(thiazino)pyrazolopyrimidines [10,11], and thiazolo(thiazino)pyridopyrimidines [12,13].…”