New Synthesis of 4,5-Dihydro-1,3-oxazoles and 4,5-Dihydro-1,3-oxazines, Useful Intermediates to Enantiomerically Pure Amino Diols. X-Ray Molecular Structure of (4S,5R,4′S)-1-(4′-Iodomethyl-4′-methyl-4′,5′- dihydro-1′,3′-oxazol-2′-yl)-