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

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.