1.3- Oxazines 2-imino-tetrahydro

As pointed out previously (Section II,B,l,e), 2-amino-5,6-dihydro-4H- 1,3-oxazines are tautomeric with 2-imino-tetrahydro-1,3-oxazines125 [Eq. (23)]. 

Other derivatives of 3-aminopropanol and 3-halogenopropylamine can also be used to form 2-imino tetrahydro-1,3-oxazine derivatives.109-112 In some instances phenylisocyanate can be used as a cyclizing agent.90... 

Not too much is known about tetrahydro-l,3-thiazines. However, 2-imino derivatives are well established compounds which exist in tautomeric equilibrium with 2-aminodihydro-1,3-oxazines (Scheme 34) (1890CB87,70TL2167). 

Meyers et al.221-222 showed that tetrahydro-l,3-oxazines exist in tautomeric ring-chain forms [Eq. (62)]. When a 5,6-dihydro-l,3-oxazine is reduced to a tetrahydro-l,3-oxazine, some 3-aminoalcohol can also be formed through the reduction of the open-chain imino form [cf. Eq. (62)]. To avoid this the reduction should be carried out with sodium borohydride at - 40°C. 

Typical examples of oxazoline monomers to be polymerized via CROP mode are shown in Scheme 3. Not only five-mem-bered monomers of ROZO and 5-oxazolones (4,5-dihydro-l,3-oxazol-5-one, ROZLO) but also six-membered analogs (5,6-dihydro-4H-l,3-oxazines, ROZI) and seven-membered ones (4,5,6,7-tetrahydro-4H-l,3-oxazepine, ROXP) have been polymerized. 2-Iminotetrahydrofurans (ITHFs) are known as an exo-cydic imino ether derivative of ROZO. CROP of ITHF was reported in 1963, which was preceded by the studies on the CROP of OZOs. Preparations of these monomers have been well known and documented. ... 

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