Optically active ketone, photolysis

Until recently, biradical intermediates were not implicated in singlet-state Norrish Type II reactions. Concerted reaction was a possibility Recovered starting material from photolysis of optically active ketones is not racemized when the photolyses are carried out in the presence of large amounts of 1,3-dienes,... 

It has been observed that the formation of the olefin and carbon monoxide, 45, is ten times more important than the formation of the bicyclic hydrocarbon and carbon monoxide, 46, at 80° and 80 mm. pressure even at 3130 A. The formation of the strained bicyclic hydrocarbon is evidently not a favorable reaction although this may not be the only consideration. In the case of camphor it should be interesting to find out if an optically active isomer of the ketone on photolysis will give rise to an optically active trimethyl bicyclo [2.1.1] hexane (XXVI). A concerted reaction, analogous to the formation of cyclobutane from cyclopentanone, may lead to only an optically active product. 

When salt crystals of the aryl 1-phenylcyclopenty 1 ketone carboxylic acid 40 with chiral amines such as (+ )-bomylamine or (—)-1-phenylethylamine were irradiated, the optically active exo- and endo-oxetanes 41 or 42 were formed in low to moderate enantiomeric excesses (Scheme 10) [57]. The formation of the oxetanes is believed to occur through Norrish type 1 cleavage and hydrogen abstraction, producing an alkene and an aldehyde, followed by a Paterno-Buchi reaction within the crystal lattice cage. In contrast, solution photolysis of 40 in acetonitrile afforded product 43 as the only isolable product via a typical Norrish type I a-cleavage followed by radical coupling. 

Amino-3-(4 -nitrophenyl)propan-l,3-diol in its optically active form has been selectively photooxidised to the corresponding ketone,and a study of the oxidation of podophyllotoxin (27) by sodium persulfate using laser flash photolysis has enabled rate constants to be determined for the formation and decay of transients. Photoinduced electrochemical oxidation of benzyl alcohol to benz-aldehyde has been achieved with 100% product selectivity and 100% current efficiency using visible radiation in the presence of riboflavin 2, 3, 4, 5 -tetraace-tate. ... 

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. 

C)5W=C(0Et)CH=C(0Et)CH=CR(02CR)]. Aldehydes or ketones react with the [diosphine complexes, [(OC)4(PR3)Cr=C(OMe)Me] to give aldol condensation products. Reaction with the amino carbene complexes [(OC)sCr=C(NMe2)Me] results in aldol addition products. Aldol reactions of optically active aminocarbene complexes proceed with moderate to high diastereoselectivity. Photolysis of chromium alkoxycaibene complexes with aldehydes in the presence of Lewis acids produces -lactones in low yield. Intramolecular reaction by incorporation of the aldehyde into either side chain of the carbene complex is considerably more efficient. ... 

Norrish Type I Reactions.— The a-cleavage of cyclic ketones to give unsaturated aldehydes has been applied successfully in several syntheses. Thus, irradiation of the cyclopentanone (154) in benzene gave the unsaturated aldehyde (155) in 77% yield." This compound was converted in four steps into the dihydroterpenediol (156), a pheromonal secretion of the African Monarch. Photolysis of the bicyclic ketone (157) in methanol gave in 60% yield the cyclobutane (158) which was converted in two steps into optically active grandisol (6)." ... 

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