1: (4-Methylphenyl)-magnesium bromide; (2R,4S,5R)-4-methyl-5-phenyl-3-(toluene-4-sulfonyl)oxathiazolidine-2-oxide in tetrahydrofuran T=-70 - -65°C; Inert atmosphere; 2: methyl-magnesium chloride in tetrahydrofuran T=-10 - 0°C; Inert atmosphere;