1.3- Thiazines from thioureas

Many workers have employed /3-haloearboxylic acids (142) to prepare tet.rahydro-l,3-thiazines (143) from thioureas. The halogen atom (X)... 

Perhydro-l,3-thiazine-2-thiones (211) can be synthesized from thioureas and 1,3-dibromo-propanes in the presence of sodium hydroxide, followed by the treatment of the product imines... 

Amino-4//- 1,3-thiazines have been obtained from a three-component one-pot condensation using alkynes, thiourea and aryl aldehydes (Scheme 67).156... 

The reaction of thiourea with acetylenic esters has been variously reported to give a thiazolin-4-one (372), an imidazolinethione (373), or a l,3-thiazin-4-one (374) " derivative. However, recent studies have shown that in fact it is the thiazolin-4-one (372) that is formed in this reaction [Eq. (55)]. In the light of this observation, it may now be necessary to revise the structures of products obtained from the reaction of A -methylthiourea, M -dimethylthiourea, and thiosemicarbazides with acetylenic esters. The reaction of a thiourea derivative such as A(-thiocarbamoylpiperidine with DMAD is reported to give 5-(carbomethoxymethylene)-2-piperidino-A -1,3-thiazolin-4-one (375) [Eq. (56)]. °... 

Perfluoro(3-isothiocyanato-2-methyl-2-pentene) reacts with N-nucleophiles to produce a series of fluoroalkyl-substituted 6/f-l,3-thiazines <1997RJO720>. The acid-catalyzed cyclization of thioureas immobilized on Wang (X = O) or Rink resin (X = NH) provides a convenient route to a wide range of 2-amino-4/7-benzothiazine derivatives 212 (Scheme 23) <20000L3667>. The thioureas are obtained in four steps from 2-nitrocinnamic acids. A general synthesis of 2-alkylidene-4-imino-l,4-dihydrobenzo-l,3-thiazines 213-215 involves treatment of 2-isothiocyanato-benzonitrile with acidic methylene compounds under basic conditions <2003SL1503>. The ( )-isomers are the predominant isomers formed. 

The preparation of pyrido[5,4-< ][l,3]thiazines by coupling of 4-halopyrimidine-5-pyrimidinecarboxylates with N-substituted thioureas was recorded in CHEC-II(1996) <1996CHEC-II(7)780>. A related approach has since been used to prepare a series of heteroannulated derivatives from the aldehyde 146, as summarized in Scheme 93... 

Aminopropanols, when reacted with cyanogen bromide, also afford 2-amino-(or imino)-dihydro-1,3-oxazines (Scheme 90) (64ZOB3427), and related thiazines are formed when allylic isothiouronium salts (207) are cyclized with trifluoroacetic acid and stannic chloride. The necessary starting materials are synthesized from aldehydes or ketones by the action of vinylmagnesium chloride and subsequent treatment of the product allyl alcohols (206) first with hydrogen chloride and then with a thiourea (Scheme 91) (77JHC717). 

Disubstituted-5,6-dihydro-l,3-thiazin-4-ones (319) are easily synthesized from A(-propenoyl-thioureas (320) through their reactions with boron trifluoride etherate, followed by basification with sodium bicarbonate (Equation (36)) <85S933>. 

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