1,2,6-Thiadiazine 1,1-dioxides reduction

Reduction of the 1,2,4-thiadiazine 1,1-dioxides 32 with sodium boro hydride in isopropanol gives the dihydro derivatives 33 (Equation 2) <1998JME2946>. 

The reduction of 3-(4-bromobenzamidoaminomethyl)-477-pyrido[4,3-< ]-l,2,4-thiadiazine 1,1-dioxide 34 with sodium borohydride in aqueous sodium hydroxide gave the 2,3-dihydro derivative 35 (Equation 3) <1997BSB781>. 

Formylation of the oxadiazolothiadiazine (45 R1 = R2 = Me), using formic acid/acetic anhydride gives the iV-formyl derivative (47) which upon reduction (Zn/AcOH) and subsequent heating gives the imidazo[l,2,6]thiadiazine (48) <77MI 714-01,81H(16)525>. This reaction (47) -> (48) occurs via a 4,5-diamino-l,2,6-thiadiazine 1,1-dioxide, (t/(44) Section 7.14.5.3) which is not isolated. 

Catalytic debenzylation of 2-benzyl-4-methyl-6 -l,2,6-thiadiazin-3(2//)-one 1,1-dioxide (165) is effected in high yield (86%) with palladium-charcoal and hydrogen over a short period (1 h) <84CCC840>. However, on prolonged treatment (12 h) debenzylation is followed by reduction of the C-4—C-5 double bond and formation of 4-methyl-5,6-dihydro-4 -l,2,6-thiadiazin-3(2//)-one 1,1-dioxide (166) (Equation (17)). 

The tetrahydro-27/-thiadiazine 1,1-dioxides (168) are accessible by reduction and regioselective deoxygenation of 4,5-dihydro-6/7-l,2,6-thiadiazine 1,1,2-trioxides (167) (Section 6.16.9.2.3.1) with sodium borohydride (Equation (18)) <90LA775>. 

The polarographic reduction of 4-arylazo-27/-l,2,6-thiadiazine 1,1-dioxides (Section 6.16.9.2.1.1) at 30 °C in methanol IM aqueous potassium chloride solution proceeds via a single two-electron transfer process corresponding to reduction of the azo group <83IJC(A)331>. 

Reactions of this type are confined to debenzylations of A-benzylated derivatives. Catalytic debenzylations of 1-benzyl-6//-l,2,6-thiadiazin-3(2//)-one 1,1-dioxides are readily effected with palladium charcoal and hydrogen <84CCC840>. However, care is needed as prolonged reaction times result in reduction of the thiadiazine ring (Section 6.16.6.7). 

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