Pyrimido -1,4-thiazepines

An example of the photodecomposition of a dithiin to give a stable dithiet, with elimination of ethylene, has been reported.206 A different reaction is preferred in the dithiins (261), which on irradiation, are converted to benzene derivatives (262) via the 1,4-dithiocins (263).207 The cyclic trimer of thio-acetophenone on irradiation in cyclohexane yields thioacetophenone.208 An initial carbon-sulfur bond homolysis is also responsible for the conversion, on irradiation in methanol, of a 3-cephem to two thiazoles,209 whereas a 1,2-alkyl migration followed by a further photochemically induced carbon-sulfur bond homolysis has been proposed to account for the photorearrangement of the sulfonium ylides (264) to the pyrimido-l,4-benzo[h]thiazepines (265).210 The novel photorearrangemenl of a 1,3-thiazine to a cyclopro-pathiazolidine has also been rationalized in terms of an initial carbon-sulfur... 

Pyrimido[5,4-/]benzo[l,4]thiazepines 105 were alkylated by the Vorbruggen reaction at the pyrimidine nitrogen. The resulting uracil derivatives 106 are inhibitors of HIV-1 reverse transcriptase (Equation 10) <1995JME2145>. 

This technique can also be used to build up benzo condensed pyrimido[4,5-6][ 1,4]thiazines and pyrimido[4,5-6][l,4]thiazepines. 

A small library of 4,5-dihydro-l,4-benzoxazepin-3(2/f)-ones was prepared by polymer assisted solution phase synthesis based on saheyhe aldehydes, a-bromoaeetie acid esters and primary amines <05MI643>. As noted previously, pyrimido[4,5-fe][l,4]-benzoxazepines (and diazepines, and thiazepines) can be accessed via a neat variation of the Pictet-Spengler cyclisation. The compounds are of interest as inhibitors of particular receptor tyrosine kinases <05JOC9629>. Liu et al. have also reported a synthesis of 5,6-dihydro-pyrimido[4,5-Z)][l,4]benzoxazepines 173, 174 based on a cyclocondensation of the imines 172 <05TL7523>. The advantage of the approach was the incorporation of poorly reactive pyrimidyl amines 170,171. 

There were examples of reactions of tetrahydropyrimidine—thione derivatives with 1,4-dielectrophiles affording pyrimido-fused 1,3-thiazepine derivatives (13JHC838). 

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