Reaction of (S)-(+)-4-amino-4-aryl-5,5,5-trifluoropentan-2-ones with α-chlorobenzyl isocyanates. Synthesis of (S)-(+)-4-aryl-6-(2-arylethenyl)-4-trifluoromethyl-3,4-dihydro-pyrimidin-2(1H)-ones