Synthesis and conformational study in solution and solid state of 1,3-dioxa-6-aza-2(O-trimethylsilyl ester)- and 1,3-dioxa-6-aza-2(hydroxy)- σ4λ4phosphacyclooctanes

Abstract

1,3-Dioxa-6-aza-2σ4λ4phosphacyclooctane 2 reacts with chlorotrimethylsilane in the presence of triethylamine to afford 1,3-dioxa-6-aza-2(O-trimethylsilyl ester) σ3λ3phosphacyclooctane 3. Compound 3 is readily oxidized with bistrimethylsilylperoxide (BTSP), sulfur and selenium to give the corresponding 1,3-dioxa-6-aza-2(O-trimethylsilyl ester) σ4λ4phosphacyclooctane oxide 4a, sulfide 4b, and selenide 4c. The 1H and 13C NMR analysis in benzene solution show that the heterocycle in 4a-c adopts the crown conformation which is asymmetric due to the restrained amide rotation. The complete proton and carbon assignation of 5c was completed by running a 1H{ 31P} experiment and COSY, NOESY, and HETCOR experiments. The molecular structure of 4b and 4c determined by X-ray diffraction are identical and confirm the crown conformation. Compounds 4a-c react with methanol to give the corresponding 1,3-dioxa-6-aza-2(hydroxy) σ4λ4phosphacyclooctane oxide 5a, sulfide 5b and selenide 5c. The NMR analysis of the compounds shows that the heterocycle adopts the crown conformation in DMSO solutions. The crown conformation is also confirmed by the molecular structure of 5a, determined by X-ray diffraction, which further demonstrates the presence of a strong hydrogen bond between the phosphate hydroxyl and the carbonyl group of neighboring molecules. The existence of this strong intermolecular interaction which leads to the formation of infinite chains for 5a, is also established for 5b and 5c by IR analysis. ©ARKAT USA, Inc.