Chemists Ring In With New Heterocycles

Cyclic organic groups containing nitrogen, oxygen, and sulfur in the ring with carbon are essential in many pharmaceuticals. Although myriad variations of these heterocycles are known, chemists are always on the lookout for practical synthetic routes to new or rare versions. Two research teams have just come up with such strategies. Béatrice Quiclet-Sire and Samir Z. Zard of École Polytechnique, in France, report an expedient route to six-membered sulfur-nitrogen ring compounds called dihydro-1,2-thiazines (Org. Lett. 2013, DOI: 10.1021/ol402973q). Only the parent compound (shown) has been prepared before. Building on their previous work on xanthate [ROC(=S)SR´] chemistry, the researchers coupled xanthates with olefins to form intermediates that undergo a ring-closing process to form substituted and fused-ring examples. Separately, R. Alan Aitken and coworkers at the University of St. Andrews, in Scotland, developed a method to prepare the six-membered oxygen-nitrogen heterocycle 1,4-oxazine (Chem. Commun. 2013, DOI:10.1039/c3cc47801g). Substituted and fused-ring 1,4-oxazines are known, but this is the first reported synthesis and characterization of the parent compound (shown). The researchers prepared the unstable compound by flash vacuum pyrolysis of a substituted 1,4-oxazine.