New chiral heterocycles: 5-[(R)-(+)-1'-methylbenzyl]-1,3,5-dithiazine and 3,7-di-[(R)-(+)-1'-methylbenzyl]-3,7-diaza-1,5-dithiacyclooctane. Conformational studies and their reactions with borane

Article abstract of DOI:10.1016/0957-4166(94)80025-1

We report herein the syntheses of a new 5-[(R)-(+)-1'-methylbenzyl)-1,3,5-dithiazine 1, the 5-isopropyl-1,3,5--dithiazine 2 and the 3,7-di-[(R)-(+)-1'-methylbenzyl]-3,7-diaza-1,5-dithiacyclooctane 3, two of them (1 and 3) are new sulfur and nitrogen heterocycles bearing a chiral N-substituent. Compounds 1 and 2 were found in conformational equilibrium when observed at rt at ¹H-270 MHz or ¹³C-67.8 MHz, when cooling a preferred chair conformation was observed with the N-substituent in the axial position. Heterocycle 3 was in an anchored crown conformation at rt. A conformational study of ring inversions for 1 and 3 was performed and their thermodynamic data were obtained, ΔG° = 48.1 ± 0.8 for 1 and ΔG° = 64.8 ± 1.2 kJ/mol for 3. The reactivity of 1-3 with BH3-THF was investigated, the N- or S-BH3 adducts were not stable, the reactions afforded cleanly the N-borane-N-dimethyl-N-alkylamine adducts. The reactions of 3 with BD3 gave the N-BD3 adduct of [CH2D]2N-CH[CH3]C6H5. An X-ray diffraction study of 3 confirmed its crown conformation with the N-substituents in pseudo-axial position.