Solid-state photoreactivity

Solid-state photoreactions of heterocycles in two-component crystals 98S1. 

Solid-state photoreactions in two-component crystals with formation of heterocycles 98S1. 

Sakamoto et al. reported an interesting example involving the solid-state photoreaction of AT-(a,p-unsaturated carbonyl)thiobenzamides 1 leading to thietane-fused p-lactam 2 (Scheme 2) [29-31]. 

Sakamoto et al. also reported the solution photochemistry for la-d, which gave the corresponding thietane-fused -lactams 2a-d as shown in Table 2 [30,31]. For tigloyl derivatives Ic and Id, P-lactams were obtained as a mixture of two stereoisomers (entries 6 and 8). The anti isomers were preferably formed, in ratios of 0.8 and 0.7, respectively. In the solid-state photoreaction of... 

In contrast to the solution photochemistry, irradiation of the crystals of le provided remarkably high diastereoselectivities in the formation of 2e. The temperature at which the reaction occurs is important in determining dia-stereoselectivity. At 15 °C, the de of syn-2e was 61 % and the ratio of syn/anti was 8.7, which was the reverse of that in the solution reaction (syn/anti=0.9). The solid-state photoreaction proceeded even at -78 °C, and with higher diastereo-selectivity. At low conversion (9%), only syn isomers (de=93%) were obtained, and 71% de was observed even at 90% conversion. 

The stereoselective generation of the chiral center is exemplified by the formation of 5b at the C4 position, and optically active 4b was obtained in 10% ee. The solid-state photoreaction also proceeded at -78 °C and an optically active compound which showed a better ee value was formed, 20% ee at 84% conversion (entry 6) and 31% ee at 15% conversion (entry 7). The space group of the crystal of 3a could not be determined because 3a did not afford single crystals suitable for X-ray crystallography however, the production of racemic 4a shows that the crystals are achiral (entries 2 and 3). 

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... 

Table 6 Solid-state photoreaction of 6 followed by acetylation ...

Sakamoto et al. reported the X-ray crystallographic data and the solid-state photoreaction of eight Ar,AT-disubstituted a,p-unsaturated thioamides 23a-h, which involves hydrogen abstraction by the alkenyl carbon atom conjugated with thiocarbonyls (Fig. 9) [44-46]. 

In the solid-state photoreaction of 24c, a more chemoselective reaction occurred and only p-thiolactam 25c was obtained almost quantitatively. Of particular importance is the finding that the solid-state photoreaction of 24c involves a crystal-to-crystal nature where the optically active p-thiolactam 25c is formed in specific yield. Furthermore, the X-ray crystallographic analysis revealed that the crystals of 24c are chiral, and the space group is P2j. Irradiation of crystals at 0 °C exclusively gave optically active P-thiolactam 25c, in 81% yield at 100% conversion (entry 5). As expected, the thiolactam 25c showed optical activity (81% ee). This reaction exhibited good enantioselectivity throughout the whole reaction, where a small difference was observed in the ee value from 97 to 81% ee with increasing conversion from 20 to 100% (entries 5 and 6). The solid-state photoreaction also proceeded without phase separation even after 100% reaction conversion. The crystal-to-crystal nature of the transformation was confirmed by X-ray diffraction spectroscopy. 

Keywords Thiocarbonyl Solid-state photoreaction [2+2] Cycloaddition ... 

Keywords Crystal engineering Solid-state photoreaction Topochemical polymerization Controlled radical polymerization Dimerization Isomerization Topotactic reaction... 

Solid-state photoreaction pathways are dependent on the structiue of 1,3-diene compounds as the reactant (i.e., molecular packing in the crystals) cyclodimer, 1,4-polymer, or EE isomer is produced depending on the structiue of the substituent X and the molecular packing in the crystals, as shown in Scheme 1 and Table 1. Here, the stereochemical structure of the products is highly regulated during the photoreactions in the crystalhne state. 

Scheme 1 Possible pathways for the solid-state photoreactions of (Z,Z)-diene compounds...

Table 1 Stereospecific solid-state photoreaction of (Z,Z)-muconic acid derivatives depending on the structure of alkyl substituents ...

Scheme 2 Solid-state photoreactions of some muconic and sorbic derivatives reported in 1967 and 1971 [19,201...

Yang S-Y, Naumov P, Fukuzumi S (2009) Topochemical limits for solid-state photoreactivity by fine tuning of the n-it interactions. J Am Chem Soc 131 7247-7249... 

Most solid-state photoreactions that have been reported involve photoredox, although examples of photoisomerization and photoaquation involving lattice water have also appeared. For example,... 

The solid-state photoreaction of thioamide 1 was done under an atmosphere purged with dry argon. The solid sample was irradiated for 4 h as a powder prepared by grinding, and placed inside a Pyrex slide. When powdered thioamide 1 was irradiated in the solid state at 0 °C, at up to 19% conversion, optically active /i-thiolactam 2 of 31% ee was isolated. The optical purity was determined by HPLC using a chiral cell OD column (Daicel Chemical Ind.). 

Synthesis of thietane-fused (1-lactam was reported by Sakamoto et al. [212] involving solid-state photoreaction of /V-(a,(5-unsatu rated carbonyl) thiobenzanilide demonstrating a single-step photochemical route to (5-lactam, as outlined in Scheme 52. 

Albini A, Alpegiani M, Borghi D, Del Nero S, Fasani E, Perrone E. Solid state photoreactivity of a dioxolenonemethyl ester. Tetrahedron Lett 1995 36 4633-4636. 

B. Prass, J. P. Colpa, and D. Stehlik, Chem. Phys., 136,187 (1989). Intermolecular H-Tunnel-ing in a Solid State Photoreaction Promoted by Distinct Low Energy Fluctuation Modes. 

Figure 5 Solid-state photoreaction of -cinnamic acid to produce (i-truxinic acid.

---