Pyrimidine-2-thiones

The bicyclic compounds obtained from unsymmetrical pyrimidine-thiones (104,107, and 110) can be represented by either structures 105 or 106 (50BRP634951), 108 or 109 (83M13), and 111 or 112 (75FRP22337I, 75GEP2317109 76JAP74126828), respectively (Scheme 24). No characterization of the cyclized products was attempted although cyclized product obtained from 104 was used in the preparation of merocyanine dyes (50BRP634952). 

In addition to several general reviews on enamine chemistry, all of which include heterocyclic syntheses, there is an extensive survey by Hickmott which is entirely concerned with the formation of heterocycles. More specialized reviews deal with heterocyclic enamines, enaminones, the photochemistry of enamides , heterocyclic jS-enamino esters , enamino thiones , the synthesis of indole alkaloids via enamines , formation of pyrimidines, pyridopyrimidines, pyridines and pyrrolizines from enamines , synthesis of lactams , formation of heterocycles from cyclic enamino ketones and 2-acetylcyclohexen-l-ones, the synthesis of 3-cyano-2(l -pyrimidine-thiones and -selenones from jS-enamino ketones and the chemistry of cyclic en-aminonitriles. ... 

A useful conversion of a nucleoside 2,6-dithione into a 6-methylamino-adenosine via oxidation with dimethyldioxirane, illustrates several instructive points. The presumed intermediates are sulfinic acids the 2-sulfinic acid loses sulfur dioxide to leave hydrogen at C-2, and nucleophilic displacement of the 6-sulfinic acid (or possibly the sulfonic acid after further oxidation) introduces the amino group. Similar reactions can be carried out on pyrimidine thiones. The scheme shows intermediates derived from a disulfinic acid - it is not clear in what order oxidations/loss of sulfur dioxide/displacements take place. 

The quantum yield for photodimerization of thianaphthene 1,1-dioxide is enhanced in the presence of bromoethane.188 The increase is not due to solvent polarity it does, in fact, appear to be the result of enhanced intersystem crossing to the reactive triplet. Cycloaddition reactions of the thione group have also attracted attention, particularly those occurring in pyrimidine thiones. The isolation of thietans, previously proposed as intermediates in the photoaddition of electron-deficient alkenes to thiouracil derivatives, has now been realized 187 in this way, for example, the dihydrouracil (259) is converted into the adduct... 

Another example of annelation was demonstrated by Hoffmann-La Roche at the thiazolo[4,5-d]pyrimidine scaffold synthesis and decoration. Under thionation with P2S5, the acylated 6-aminopyrimidine 195 gives the corresponding thioamide, which cyclised spontaneously into thiazolo[4,5-d]pyrimidine thione 196. Thione 196 was used further transformation for synthesis of key building block 197 applied for the preparation of the library 198 (Scheme 42) [185]. 

Treatment of 2-imino-3-phenyl-4-amino-(5-amido)-4-thiazoline with isocyanates or isothiocyanates yields the expected product (139) resulting from attack of the exocyclic nitrogen on the electrophilic center (276). Since 139 may be acetylated to thiazolo[4,5-d]pyrimidine-7-ones or 7-thiones (140). this reaction provides a route to condensed he erocycles (Scheme 92). 

Pyrimidine-4/6-thiones (and occasionally 2-thiones) can be made by thiation of the corresponding pyrimidinones providing that there are no sensitive groups present. The method is summarized and exemplified in Section 2.13.2.2.7/). 

The thiolysis of halogenopyrimidines is a valuable route to pyrimidine-2(and 4/6)-thiones and to extranuclear thiols but it fails with 5-halogenopyrimidines. The process may be... 

The preparation of quinazoline-2(and 4)-thiones follows those of the corresponding pyrimidines (67HC(24-1)270) but there is at least one special primary synthesis for quinazoline-4(3H)-thiones, illustrated by the reaction of o-aminobenzonitrile with thioacetic acid at 110 °C to give 2-methylquinazoline-4(3H)-thione in 90% yield (53JA675). 

In aqueous alkaline conditions with chloroacetic acid the pyrido[4,3- f]pyrimidinethione (80) undergoes facile ring opening, attributed to the resonance stabilization of a delocalized covalent hydrate dianion intermediate (81) (82). Pyrido[2,3- f]pyrimidine-4-thiones (and... 

The thiones are readily desulfurized with Raney nickel to give the corresponding unsubstituted compounds in bicyclic systems in the 2-, 4- and 7-positions, and in tricyclic systems such as (95). The 2-methylthio derivatives may be similarly desulfurized. Thione groups in the 4-position, but not the 2-position, in pyrido-[2,3- f ]- and -[3,2- f]-pyrimidines may be replaced directly with ammonia or amines. 

Pyrimido[5,4-d]pyrimidine-2,4,6,8-tetrone X-ray, 3, 339 (66JCS(A)639> Pyrimido[4,5-d]pyrimidine-4-thione pK 3, 339 (58JOC1451) Pyrimido[4,5-d]pyrimidine-2,4,7-triamine,... 

Pyrido[2,3-d]pyrimidine-2-thione, 7-phenyl-reactions, 3, 211 Pyridopyrimidinethiones reactions, 3, 213 Pyrido[2,3-d]pyrimidinethiones reactions, 3, 213... 

Pyrimidine-2-thione, 4,5-diamino-S-alkylation, 3, 94 Pyrimidine-2-thione, dihydrosynthesis, 3, 109... 

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