Mono- and di-alkyl-[1,3,5]-dithiazinanes and their N–borane adducts revisited. Structural and theoretical study

Structural analyses of a series of 5-alkyl-[1,3,5]-dithiazinanes [R = Me (1), iPr (2), tBu (3)], their N–BH3 adducts (1BH3–3BH3) and their 2-alkyl (R′) derivatives are reported: R = Me, R′ = Me (7); R = Me, R′ iPr (8); R = iPr, R′ = Me (10); R = tBu, R′ = Me (11); and R = Me, R′ = nBu (12). The reaction of 2-lithium-5-methyl-[1,3,5]-dithiazinane (4) with I2 affords the bis-(5-methyl-[1,3,5]-dithiazinan-2-yl) (13). Isostructural compounds: [2,5,5]-trimethyl-[1,3,5]-dithiazinan-5-ium iodide (14), 5-borane-2,5-dimethyl-[1,3,5]-dithiazinane (15) and 2,5,5-trimethyl-[1,3,5,6]-dithiazaborata (16) are compared. Structures of 7, 8 and 10–13 were determined by 11B, 13C and 1H NMR and the X-ray diffraction analyses of 2, 1BH3, 13 and 14 are reported. Optimization of two chair conformers of heterocycles 1–3, 1BH3–3BH3, 7, 9 (R = Me, R′ = tBu), 13–16 were performed by HF/6-31++G and B3LYP/6-31G(d,p) methods and their minimum energy is compared. 2-Alkyl substituents or N–BH3 anchor the [1,3,5]-dithiazinane ring conformation allowing the analyses of steric and electronic interactions as well as the lone pairs effect in these molecules.