Dihydro-1,4-thiazine 1-oxides synthesis

One notable advance in this chemistry since the publication of CHEC-II(1996) is the use of enantiomerically enriched 3,6-dihydro-l,2-thiazine 1-oxides in the rearrangement sequence. For instance, iV-Cbz-protected bicyclic 1,2-dihydrothiazine 44 undergoes ring opening upon treatment with phenylmagnesium bromide (Scheme 16). The synthesis of allylic amino alcohol 129 is completed in excellent yield upon exposure of the intermediate sulfoxide 130 to trimethyl phosphite and methanol at 80 °C <2002TA2407, 2000TL3743>. 

The hetero-DielsAlder reaction of A-sulfinyl 141 (X = 0 or NR) or thionitrosoarene 144 dienophiles with dienes 142 is the main method for the formation of 3,6-dihydro-2//-l,2-thiazine 1-oxides 143 or 3,6-dihydro-2//-1,2-thiazines 145 (Scheme 73) . The mechanistic and stereochemical aspects of this reaction are covered in detail in GHEC-II . In general, thionitrosoarenes 144 are transient in nature, rather difficult to prepare, and thus have a limited role in the synthesis of 1,2-thiazines. On the other hand, A-sulfinyl compounds 141 and related sulfur diimines are more stable and are isolable species. The common method of preparation of the A-sulfinyl compounds involves treatment of an amine or amide with SOCl2 and base. 

Diene synthesis with thionylimines 3,6-Dihydro-l,2-thiazine 1-oxides... 

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