A Simple Access to the Synthesis of 5,6- Dihydro-4H-1,3-oxazines Under Solvent Free Condition and Microwave Irradiation

2-Arylsubstituted 5,6-dihydro-4H-1,3-oxazines were conveniently synthesized by the condensation of 3-aminopropanol and desired carboxylic acids under solvent free and microwave conditions in short reaction times with moderate to good yields. A comparison of this method with the classical protocols using acid halides and nitrile substrates was also made. INTRODUCTION The synthetic utility of dihydro-1,3-oxazines as useful intermediate for the synthesis of ketones [1], unusual aldehydes, such as trans βinoylidene acetaldehyde [2-5], carboxylic acids, stereoselective synthesis of trans-olefins, complex heterocyclic systems and biologically active compounds has been well documented [6-8]. Recently 1,3-oxazine ring system was employed in the design of a molecular switch based on the photoinduced opening and thermal closing of the oxazine ring [9]. Several synthetic approaches to 1,3oxazine derivatives have been reported in the literatures. Some examples of these methods are: using azido-1-propanol [10], Ritter reaction consists of reacting a diol with a nitrile under strongly acidic conditions [11], synthesis utilizing nitriles and aminoalcohols in the presence of a mild Lewis acid (Cu(OAc)2, ZnCl2) as a catalyst [12], the [4+2] cycloaddition of an N-acylimine and an alkene [13], using N-acyl-4-acyloxy-βlactams under basic conditions [14], intramolecular hydroamination of trichloroacetimidate in the presence of Au(I) complex [15], cycloaddition reactions using 2-azadienes with electron-