Hydrogenation or Other Addition to the Double Bond of Unsaturated 1,3-Oxazines

Hydrogenation or Other Addition to the Double Bond of Unsaturated 1,3-Oxazines 

Numerous tetrahydro- 1,3-oxazines have been prepared by Meyers et al.2-3 by reducing 5,6-dihydro-4//-l, 3-oxazines with sodium borohy-dride. Catalytic hydrogenation of 5,6-dihydrooxazine-6-one failed to produce the tetrahydro derivative, as ring opening occurred.58 

Additions to the double bond of dihydro-1,3-oxazines can also produce bicyclic derivatives of tetrahydro-1,3-oxazines, such as 959 [Eq. (3)]. Phthaloylglycyl chloride and dihydro-1,3-oxazines in the presence 

A number of diastereoisomeric pairs of quaternary salts of 5-nitro-tetrahydro-l,3-oxazine derivatives (11a and lib) were prepared by the action of n-alkyl bromides or iodides on 5-nitrotetrahydro-1,3-oxazines.61 The products contained at the 3-equatorial position the n-alkyl derived from the alkyl bromide (or iodide), 6a and 6b [Eqs. (4) and (5)]. 

A few perchlorates of quaternary tetrahydro-l,3-oxazines were also described.82 Quaternary chlorides were prepared by direct cyclization of 3-dimethylaminopropanols with formaldehyde in hydrochloric acid.23 

---