Solid state photochemistry asymmetric induction

Table 2 Asymmetric induction in the solid-state photochemistry of compounds 29a-d ...

Scheffer and co-workers have carried out extensive research on the use of oiganic salts for, e.g asymmetric synthesis (Schemes 36-38), heavy atom effects (Scheme 39), and triplet sensitization (Scheme 40) [43a,64-73]. Chiral crystals of prochiral oiganic acids or bases were prepared by salt formation with optically active amines or acids, respectively, and the solid-state photochemistry of the resultant salts led to asymmetric induction in prochiral acids or bases. These are illustrated for the solid-state di-7C-methane photoreaction of 9,10-ethenoanthra-cene (dibenzobarrelene) derivatives (Schemes 36 and 37) [65-67] and for the Norrish type II photocylization of phenyl ketones (Scheme 38) [68-71]. Nonab-soibing, optically active amines or acids must be used as a chiral handle. Solution photolysis gave photoproducts with no optical activity. 

Cheung, E., Netherton, M. R., Scheffer, J. R., Trotter, J., and Zenova, A., Asymmetric induction through the use of remote covalent and ionic chiral auxiliaries in the solid state photochemistry of 2-benzoyladamantane-2-carboxyHc acid derivatives. Tetrahedron Lett., 41, 9673, 2000. Hashizume, D., Ohashi, Y., Tanaka, K., and Toda, F., The mechanism of the enantioselective photocyclization of 2-piperidone in the clathrate crystal. Bull. Chem. Soc. Jpn., 67, 2383, 1994. 

Cheung, E., Rademacher, K., Scheffer, J. R., and Trotter, J., An investigation of the solid state photochemistry of a-mesitylacetophenone derivatives asymmetric induction studies and crystal structure-reactivity relationships, Tetrahedron, 56, 6739, 2000. 

Gudmundsdottir, A. D. and Scheffer, J. R., Asymmetric induction in the solid state photochemistry of salts of carboxylic acids with optically active amines. Tetrahedron Lett., 31, 6807,1990. 

Scheffer JR, Xia W (2005) Asymmetric Induction in Organic Photochemistry via the Solid-State Ionic Chiral Auxiliary Approach. 254 233-262 Schenning APHJ, see Ajayaghosh A (2005) 258 83-118 Schepers U, see Hahn F (2007) 278 135-208 Schindler J, see Faigl F (2007) 269 133-157... 

Covalent Chiral Auxiliary-Induced Asymmetric Induction in Solid-State Organic Photochemistry... 

Asymmetric Induction in Organic Photochemistry via the Solid-State Ionic Chiral Auxiliary Approach... 

Abstract After a brief introduction and summary of various methods of asymmetric induction in organic photochemistry, the main part of the review covers the solid-state ionic chiral auxiliary approach to asymmetric photochemical synthesis. Application of this technique to the Norrish type II reaction, as well as to the di-n-methane and oxa-di-n-methane photorearrangements, and the cis,trans-photoisomerization of diarylcyclopropane derivatives is presented and discussed. 

Keywords Asymmetric induction Organic photochemistry Solid state ... 

One reason that salts of general structure 7 were chosen for investigation is that molecular mechanics calculations showed the benzocyclohexadienone framework to be planar. This planarity translates into an equal opportunity of forming either enantiomer of photoproduct 8, or to put it another way, the photochemistry of these salts is conformationally unbiased with respect to enantioselec-tivity. As a result, any ee in the crystalline state would have to be due to an essentially pure topochemical effect. Only one of the salts investigated (7b) gave a respectable ee in the solid state, and unfortunately, it has not been possible to obtain an X-ray crystal structure of this material, thus precluding an analysis of the specific topochemical factors responsible for asymmetric induction in this case. 

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