Photodecarboxylative condensation solid state

Photoirradiation of chiral salt crystals formed from base 48 and acid 49 in the solid state gave the optically active product 50 of about 35% ee in 37% yield via photodecarboxylative condensation reaction [27],... 

When two different achiral molecules form a chiral cocrystal by spontaneous chiral cocrystallization, the occurrence of absolute asymmetric intermolecular photoreaction can be expected. In fact, we have achieved enantio- and diastereo-selective photodecarboxylative condensation, as well as absolute asymmetric pho-todecarboxylative condensation. The development of intermolecular photoreao tions leads to an extension of the scope of solid-state chiral photochemistry. Reactivity in a cocrystal is controlled by the crystal packing arrangement, so the key point is the preparation of photoreactive cocrystals. 

Irradiation of the M-crystals caused solid-state photodecarboxylation, and then enantioselective condensation occurred, to give the optically active condensation product (S)-( —)-151 as the main product with [a] = —30 in 35% ee and in 37% chemical yield (Scheme 35). Conversely, irradiation of the P-crystals resulted in formation of the opposite handed condensation product (/ )-(+ )-151 with [a]r = +30 in 33% ee and in 38% chemical yield. For a comparison, solution phase photolysis of acridine 150 and diphenylacetic acid DPA in acetonitrile did not produce chiral product 151 but rather gave the achiral condensation product 153 in 74% as the major product at complete conversion of DPA. 

On the subject of spontaneous generation of chirality, it is of interest to know that spontaneous formation of chiral aggregates from nonchiral monomers is known to occur, e.g. the assembly of tetra-alkyl benzimidocyanins 3 as monitored by CD (circular dichroism). Formation of chiral crystals from achiral monomers is also reported, e.g. by photodimerization in the solid state. " In a recent example, chiral crystals of acridine 4 and diphenylacetic acid 5 give excess of the (.S)-product 6 upon a photodecarboxylating condensation reaction. Symmetry breaking is also known to occur for supramolecular complexes of achiral components e.g. glu-tarimide 7 and the diaminopyridine 8, and, as will be discussed below, in monolayers at the air-water interface. ... 

Solid-state irradiation of two component molecular crystals of thienylacetic acids with aza aromatic compounds (acridine and phenanthridine) ° results in photodecarboxylation and gives decarboxylated and condensation products. Two-component molecular crystals of the above azo aromatic compounds with 3-indolepropionic acid and 1-naphthylacetic acid, upon solid-state irradiation, give radical intermediates via electron transfer and ultimately afford decarboxylated compounds in near quantitative yield. Irradiation of crystalline charge-transfer complexes of 3-indoleacetic acid and 2-naphthylacetic acid with 1,2,4,5-tetracyanobenzene gives methylnaphthalene (decarboxylation) and naphthyl(2,4,5-tricy-ano)methane (dehydrocyanating condensation) in the solid state. 

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