Synthesis and Alkylation of N-Methylmorpholinium 4-Aryl-3,5-dicyano-6-oxo-1,4,5,6-tetrahydro-2-pyridinethiolates. Molecular and Crystal Structure of 4,5-trans-3,5-Dicyano-4-(2-methoxyphenyl)-2-methylthio-6-oxo-1,4,5,6-tetrahydropyridine