1-Organosulfonyl-2-sila-5-piperazinones: Synthesis, molecular and crystal structure, and chemical transformations into 2-aminoacid derivatives

Abstract The reaction of chloro(chloromethyl)dimethylsilane and hexamethyldisilazane with N -methylamides of N ′-organosulfonyl-2-amino acids ( 1a – e ), the derivatives of N -mesylglycine ( a ), N -tosylglycine ( b ), N -nosylglycine ( c ), N -nosylalanine ( d ) and N -nosylleucine ( e ), affords new type of silacyclanes, 1-organosulfonyl-2-sila-5-piperazinones 2a – e . The presence of very labile Si–N bonds in compounds 2 can be utilised in a variety of synthetic applications. The hydrolysis of 2a – e yields disiloxanes 3a – e , which can be subsequently transformed into fluorosilanes, such as 4a , by the reaction with boron trifluoride. Ring-opening reactions of piperazinones 2b with 1-chloromethyl-2-pyrrolidone and acetyl bromide lead to previously unknown silyloxonium chloride 6b and silyloxonium bromide 8b , respectively, containing fragments of 2-amino acids as C,O-chelate ligands. Crystal structures of N -methylamide 1b , piperazinones 2a , d , e , disiloxanes 3c , e , fluorosilane 4a , silyloxonium chloride 6b and silyloxonium bromide 8b have been determined by X-ray diffraction study. The silicon atom in piperazinones and disiloxanes is tetracoordinated while compounds 4a , 6b and 8b contain pentacoordinated Si atoms.