Nature Chooses Rings: Synthesis of Silicon-Containing Macrocyclic Peroxides

The reactions of 1,2-bis(dimethylchlorosilyl)ethane (1), 1,2-bis(dimethylchlorosilyl)ethene (6), and 1,2-bis(dimethylchlorosilyl)ethyne (7) with gem-bis-(hydroperoxides) 2a-h and 1,1'-bis( hydroperoxy)bis-(cycloalkyl)peroxides 4a-c were found to proceed in an unusual way. Thus, the reactions do not give the expected polymeric peroxides; instead, they produce cyclic silicon-containing peroxides containing 2, 4, or 6 silicon atoms in the ring: 9- (3a-h), 12- (5a-c), 18- (8, 12), 24- (9, 10), 27- (13), and 36-membered (11) compounds. The size of the rings produced in the reactions increases in the series 1,2-bis(dimethylchlorosilyl)ethane < 1,2-bis(dimethylchlorosilyl)ethene < 1,2-bis(dimethylchlorosilyl)ethyne. The resulting 9- and 12-membered cyclic peroxides are stable under ambient conditions. These compounds were isolated by chromatography and characterized by H-1, C-13, and Si-29 NMR spectroscopy, X-ray diffraction, elemental analysis, and high-resolution mass spectrometry. The yields vary from 77 to 95%. Structures of the larger-size rings (18-, 24-, 27-, and 36-membered peroxides) were confirmed by H-1, C-13, and Si-29 NMR spectroscopy using 2D (COSY, HSQC, and HMBC), 2D DOSY H-1, 3D H-1-Si-29 HMBC-DOSY NMR experiments, and elemental analysis.