Aminoketone irradiation

An unusual approach to the lumazine nucleus was found in the photochemical transformation of 6-azido-l,3-dimethyluracil (289) with various amino compounds (78JA7661). Irradiation of (289) in the presence of ethyl a-amino acid esters forms 7-substituted 7,8-dihydrolumazin-6-ones (288), and with a-aminoketones 6-substituted 7,8-dihydro-lumazines (290) are formed (equation 103). 

Attempts to isomerize the 2-methylene-3/f- azepine (45 R1 = H, R2 = PhCO) to the AT-benzoyl- 1H-azepine under acid- or base-catalyzed conditions failed. Irradiation of the 3//-azepine resulted only in a photo-Fries type rearrangement of the benzoyl group to give aminoketone (45 R1 = PhCO, R2 = H) (74JOC3076). 

Irradiation of 2-cyanonaphthalene in the presence of 2,3-dimethyl-1,3-butadiene yielded (4 + 4) cycloadducts (70, 71) onto the naphthalene ring (Scheme 25). The main product from the reaction of 2-cyanonaphthalene with cyclohexa-1,3-diene is the (2 + 2) adduct (72), whereas a minor product is the (4 + 4) adduct (73). The reaction with 2,5-dimethyl-2,4-hexadiene leads again to a (2 + 2) cycloadduct (74) and aminoketone (75). 

By contrast, irradiation in benzene of P-aminoketones having a secondary amino group produces photopinacolizatiorf with formation of the diols 372. 

The reaction was applied successfully to cyclic vinyl azides to produce fused azirine rings. 1-Azido-cyclooctene (46) was converted on irradiation in 93% yield into 9-azabicyclo-[6.1.0]-non-l-(9)-ene (47). The azirine could again be hydrolysed to the aminoketone (48)... 

Light induced electron transfer from an amine to an excited arene leading to a contact radical ion pair is proposed to account for the products observed when 9,10-dicyanoanthracene is irradiated in wet benzene in the presence of an a-aminoketone. The non-polar solvent maintains the proximity of the radical ion pair which would normally then undergo non-productive back electron transfer however, in this case the ion pair reacts, ultimately to furnish 9,10-dihydro-9,10-dicyanoanthracene along with products of fragmentation of the a-aminoketone. Alkyl borate and borohydride salts can also serve as electron donors in the photoreduction of aryl cyanides and aryl halides and an abstract of a report on this topic has appeared. ... 

Selective formation of an optically active cyclobutanol has been achieved in type II cyclization of salts of aminoketone 18 (Scheme 7). While irradiation of the free aminoketone in benzene gives c-19 (c ) = 0.105), t-19 (0.048), and 20 (0.120), little or none of t-19 is produced when the salts formed between 18 and enantiomerically pure acids are photolysed in the crystalline state (Table 55.6). Enantiomeric excesses obtained for c-19 are fairly good except for the iV-Cbz-L-phenylalanine salt of 18. The decrease in enantioselectivity with increasing conversion is due to the breakdown of the ordered crystal lattice as photoproducts replace starting material. The solid-state ionic chiral auxiliary approach may become one of general techniques for asymmetric synthesis in organic photochemistry. 

The influence of electronic effects on aminium radical a-CH kinetic acidities has been observed in product distribution studies of Mariano and co-workers." These workers found that irradiation of (3-aminoethyl-substituted cyclohexenones 12 leads to formation of mixtures of regioisomeric products 14. The SET promoted photocyclization reactions proceed via the intermediacy of zwitterionic biradicals 13. Intramolecular proton transfer between the aminium and enone anion radical moieties in 13 is followed by radical coupling to give spirocyclic aminoketones 14 (Scheme 11). The relative rates of aminium radical... 

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