1.3.5- Oxadiazines, from thioureas

The only preparation of a ring system of this type from thioureas, which has been reported in the literature, is the tetrahydro-1,3,5-oxadiazine series of Seidel and Boettner,302 who synthesized compounds 171 by treating thioureas with formaldehyde in the presence of p-toluenesulfonic acid. 

Synthesis of 1,3,5-oxadiazines from acyl azides consists of treatment of the acyl azides 187 with urea or thiourea at 170 °C to afford the l,3,5-oxadiazin-4-ones 188a and 188b by diazido displacement with subsequent cyclization (Scheme 31) <1998MI91>. 

Carboxamides form rather unstable 1 1 adducts with HFA insertion into one N—H bond occurring as with urea 202). Addition of another molecule of HFA can only be effected by salt formation with pyridine. The addition is reversible. A stable product 125a is obtained from urea in the presence of acetic acid anhydride 257). Thiourea forms the corresponding oxadiazin-thione 125b with HFA (257). 

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See also in sourсe #XX -- [ , ]

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