Hydrogen abstraction, in the solid state

Absolute Asymmetric Transformation via Hydrogen Abstraction in the Solid State... 

Other simple carbonyl compounds that undergo photochemical hydrogen abstraction in the solid state are, e.g., a-cyclohexyl-acetophenones (21), a-adamantylacetophenones (9), N,N-dialkyl-a-oxoamides (22), and 2-tert-butylbenzophenones (23). Norrish Type I and Type II reactions of phenyl alkyl ketones included in various hosts have been studied to examine medium-effects on product distributions (24). 

Sakamoto et al. provided the first example of hydrogen abstraction by thiocarbonyl sulfur in the solid state [37,38]. Irradiation of AT-diphenylacetyl-AT-iso-propylthioaroylamides 6 in the solid state gave thioketones 7 (P-hydrogen abstraction products by thiocarbonyl sulfur), mercaptoazetidin-2-ones (y-hy-drogen abstraction products by thiocarbonyl sulfur), and aroylthioamides (y-hydrogen abstraction products by thiocarbonyl sulfur followed by cleavage). 

Irradiation of the powdered crystals of 6a-d with a high-pressure mercury lamp under argon at 0 °C showed a different photochemical behavior from that in benzene solution. Contrary to the photochemical results in solution media in which azetidin-2-ones 8 (y-hydrogen abstraction products) were formed as major products, thioketones 7 (P-hydrogen abstraction products) were obtained as major components in the solid-state photoreactions (Scheme 7). The... 

Scheffer et al. also reported hydrogen abstraction of thioketones in the solid state [42]. The nTi" and 7171" excited states differ in the spatial properties of the orbitals involved in abstraction, and it follows that ketones and thiones should exhibit significantly different hydrogen atom abstraction geometries. 

Hydrogen Abstraction by Thiocarbonyl Groups in the Solid State.218... 

Presumably, the same steric factors that discourage formation of the other two isomers in solution are operative in the solid state. In addition, the reaction cavity of the solid places clear conformational constraints upon which y-hydrogen atom can be abstracted 91 and 93 have a common BR precursor 90 and 92 emanate from a different BR conformer. The control is selective, but not specific. 

Sakamoto et al. provided an example of absolute asymmetric synthesis involving hydrogen abstraction by thiocarbonyl sulfur (Scheme 6). [24] Achiral A -diphenylacetyl-iV-isopropylthiobenzamide 33 and Y-diphenylacetyl-A-isopropyl(p-chloro)thio-benzamide 33 crystallize in chiral space group P2 2 2. Photolysis of the chiral crystals in the solid state gave optically active azetidin-2-ones whereas achiral thioketones were obtained as main products. When 33a was irradiated in the solid state at -45°C followed by acetylation (at -78°C), 2-acetylthio-3,3-dimethyl-l-diphenylacetyl-2-phenylaziridine (34a 39% yield, 84% ee), 4-acetylthio-5,5-dimethyl-2-diphenylmetyl-4-phenyloxazoline (35a 10% yield, 50% ee), 3,3-diphenyl-1-isopropy 1-4-... 

Sakamoto and co-workers have explored a very interesting photochemical method for the preparation of p-lactams [95JOC7088], The reaction proceeds through a hydrogen abstraction from achiral acyclic monothioimide 11. When the photolysis is conducted in the solid state, absolute asymmetric induction takes place and the lactam 13 is produced with low enantiomeric excess. 

Sakamoto et al. have provided an example of absolute asymmetric synthesis involving [i-hydrogen abstraction by thiocarbony] sulfur (Scheme 4.68) [102]. The achiral benzothioamides 126 crystallize in chiral space group P212121. When the chiral crystals were irradiated in the solid state at —45 °C, followed by acetylation with AcCl at —78 °C, the aziridines 127 were obtained as a main product in a highly enantioselective cyclization. 

Absolute asymmetric synthesis using the chiral crystal environment photochemical hydrogen abstraction from achiral acyclic monothioimides in the solid state. Journal of Organic Chemistry, 60 (22), 7088-7089 ... 

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