Synthesis and Reactions of Ketenimines

The Reactivity of (Z)‐5‐Acetyl‐3‐aryl‐2,3‐dihydro‐2‐[(thioacyl)methylene]1,3,4‐thiadiazoles: A Surprising Base‐Induced Conversion into 3‐(N‐arylamino)thiophenes

“…200°C, 5.70 g, 71%). Preparation of [1,2-13 C]Thioacetamide: A mixture of [1,[2][3][4][5][6][7][8][9][10][11][12][13] C]acetamide having 5% isotopic abundance (5.65 g), P 2 S 5 (4.40 g) and K 2 S (9.50 g) in toluene was heated at 75Ϫ80°C with stirring for 1 h, and then the toluene was decanted. This sequence was repeated seven times.…”

“…1 H NMR: δ ϭ 7.30 (m,8 H),7.16 (d,4 H),7.08 (t,1 H),6.78 (d,2 H),5.14 (s,1 H),3.87 (s,3 H) NO (301.4): calcd. C 83.69,H 6.35,N 4.65;found C 83.71,H 6.32,N 4.50. Preparation of [1,2-13 C]Acetamide: A mixture of [1,[2][3][4][5][6][7][8][9][10][11][12][13] C]acetic acid having 5% isotopic abundance (8.15 g) and urea (7.25 g) was heated at 200°C on an oil bath. Heating was continued until gas evolution stopped, and then the mixture was distilled to give the title compound (b.p.…”

“…The (thioacetyl)keteneimine 5 could undergo either a further alkoxide attack, affording 3a,b, or give 4 through a [4ϩ2] cycloaddition process involving the heterodiene system of 5 and the thiocarbonyl group of 3a as the dienophilic unit. It is known that keteneimines undergo both nucleophilic additions at the imino group's carbon atom [2] and [4ϩ2] cycloaddition reactions with the thiocarbonyl group. [3] The formation of a keteneimine similar to 5 by alkaline cleavage of a 5-acetyl-2-methylenethiadiazole system was demonstrated in the case of the structurally simpler substrates 6a,b.…”

The crystal structure of 2-diphenylmethyl-4,4-diphenyl-6-methyl-4H-3,1-benzothiazine

“…While the most common reactivity mode of ketenimine cycloaddition is that occurring on the cumulative C=C or C=N double bond (Krow, 1971), the formation of (III) the 3,1-benzothiazine must involve the cumulene system and the C=C bond of the N-aryl ring. In order to provide an unequivocal structure assignment of the observed products, we have carried out the crystal structure determination of the title compound (III) derived from the reaction of thiobenzophenone (I) and diphenyl-N-p-tolylketenimine (II).…”

A Mechanistic Rationale for the Mode Selectivity in the Intramolecular Cyclization of Ethylene‐Tethered Iminoketenimines: [2+2] versus [4+2] Stepwise Cycloadditions

“…We have calculated the relative ratio of products 9 and 10 that this theoretical treatment predicts by performing a quantitative kinetic analysis that considers the system represented by Equations (1) and (2). From the computational results, we can assume that [exo-INTc] ϽϽ [9] and [endoINTc] ϽϽ [9] ϩ [10], and, consequently, the steady-state approximation [41] can be applied [Equations (3) and (4) yielding Equations (5) and (6)].…”