New Models for the Study of the Racemization Mechanism of Carbodiimides. Synthesis and Structure (X-ray Crystallography and ¹H NMR) of Cyclic Carbodiimides

Abstract

The crystal and molecular structure of carbodiimides 2 (5,6,18,19-tetradehydro-5,12,13,18,25,26-hexahydrotetrabenzo[d,h,m,q][1,3,10,12]tetraazacyclooctadecine) and 3 (8,10,22,24-tetraazapentacyclo[23.3.1.1(3,7).1(11,15).1(17,21)]dotriaconta-1(29),3,5,7(32),8,9,11,13,15(31),17,19,21(30),22,23,25,27-hexadecaene) have been determined. The activation barriers for the racemization of carbodiimides 1 (6,7-dihydrodibenzo[d,h][1,3]diazonine), 2, and 3 have been determined. While 1 presents a relatively high barrier (17.4 kcal mol(-)(1)), 2 and 3 have very low activation barriers (between 5 and 7 kcal mol(-)(1)). We tentatively conclude that open-chain and large-ring carbodiimides racemize by nitrogen inversion or trans-rotation while medium-size cyclic carbodiimides racemize by cis-rotation.

Exploring the Potential of 2-(2-Nitrophenyl)ethyl-Caged N-Hydroxysulfonamides for the Photoactivated Release of Nitroxyl (HNO)

“…The elimination (C–O/N–S or C–O bond cleavage) and O–N cleavage photolysis pathways shown in Scheme were expected to generate byproducts 2-nitrostyrene ( 2 ) and 2-nitrophenylacetaldehyde ( 10 ), respectively. Through independent synthesis (Scheme ) − and analyses, we were able to identify the presence of both 2-nitrostyrene ( 2 ) and 2-nitrophenylacetaldehyde ( 10 ) as the primary photolysis byproducts.…”

“…The organic solution was dried over MgSO 4 and filtered, and the filtrate was concentrated in vacuo . The resulting dark brown oil was purified by flash column chromatography (silica gel/1:1 CH 2 Cl 2 /petroleum ether) to afford the title compound as a yellow oil (0.376 g, 26%): 1 H NMR (400 MHz, CDCl 3 ) δ 9.85 (t, J = 0.9 Hz, 1H), 8.15 (dd, J = 8.0, 1.6 Hz, 1H), 7.63 (td, J = 7.5, 1.4 Hz, 1H), 7.53–7.48 (m, 1H), 7.33 (dd, J = 7.6, 1.5 Hz, 1H), 4.12 (br s, 2H) …”

“…The resulting dark brown oil was purified by flash column chromatography (silica gel/1:1 CH 2 Cl 2 /petroleum ether) to afford the title compound as a yellow oil (0.376 g, 26%): 1 H NMR (400 MHz, CDCl 3 ) δ 9.85 (t, J = 0.9 Hz, 1H), 8.15 (dd, J = 8.0, 1.6 Hz, 1H), 7.63 (td, J = 7.5, 1.4 Hz, 1H), 7.53−7.48 (m, 1H), 7.33 (dd, J = 7.6, 1.5 Hz, 1H), 4.12 (br s, 2H). 49 2-(Methanesulfonyl)benzenesulfonamide (12). Aqueous ammonia (35% solution, 1.2 mL) was added all at once to a stirred suspension of 2-(methanesulfonyl)benzenesulfonyl chloride (0.247 g, 0.970 mmol) in diethyl ether (30 mL) at 3 °C in an ice bath.…”

Conformation of 5,6,11,12-tetrahydrodibenzo[a,e]cyclooctene: an experimental and theoretical NMR study

“…To these two conformations correspond a set of coupling constants (the vicinal ones following the Karplus relationship) that can be used to reproduce the lineshapes at di †erent temperatures. 11). The variable temperature was computer-controlled and the internal temperature calibrated by employing the methanol thermometer method.…”

Substituent effects on the stability of carbodiimides

“…Optical isomerism in such compounds is possible but resolution has not been achieved because of the low free energy barrier to racemization. [5][6][7][8][9][10][11] Semiempirical quantum mechanical calculations (INDO) predict the intuitively favored asymmetric geometry with substituents in perpendicular planes that intersect along the N᎐ ᎐ C᎐ ᎐ N axis. 5 The calculated energy for thermal racemization of carbodiimides and difluorocarbodiimides are 8 and 22 kcal mol Ϫ1 , respectively.…”