Photocyclization reductive

A wide range of 4-thio-substituted 2-aryl-4H-chromenes is formed when 2-hydroxychalcone derivatives react with various thiols (Scheme 27). Two new C-S and C-O bonds are formed in this catalyst-free domino reaction (13T2430). Chiral phosphoric acids catalyze the photocyclization reduction of 2-hydroxychalcones (13CEJ13658) and the 1,4-reduction of racemic 2,4-diaryl-2H-chromen-2-ols (13CEJ9775), both in the presence of the Hantzsch ester, to provide 2,4-diaryl-4H-chromenes in good yields and with excellent enantioselectivity. 

Liao HH, Hsiao CC, Sugiono E, Rueping M (2013) Shedding light on Brpnsted acid catalysis a photocyclization-reduction reaction for the asymmetric synthesis of tetrahydroquinolines from aminocalchones in batch and in flow. Chem Commun 49 7953-7955... 

Some natural products (209), (212), (214), (216), and (218) were synthesized by intramolecular photocyclization as a key step in synthetic plans (Schemes 41-44). Asymmetric photocyclization-reduction reaction of aminochalcones (219) in the presence of chiral Bronsted acid... 

Dynamic nuclear polarisation (DNP) enhanced 15N CP MAS NMR has been exploited by Mark-Jurkauskas et al.79 in the studies of intermediates of the bacteriorhodopsin photocycle. The data for L intermediate were similar to those found for 13-ds,15-anti retylidene chloride, while those for K intermediate were similar to those of acid blue bacteriorhodopsin in which the Schiff base counterion was neutralised (Table 3). The 15N chemical shifts observed have shown that for bacteriorhodopsin, the Schiff base in K intermediate state loses contact with its counterion and establishes a new one in L intermediate state. The proton energy stored at the beginning in the electrostatic modes has been transformed to torsional modes. The transfer of energy is facilitated by the reduction of bond order alternation in the polyene chain when the counterion interaction is initially broken and is driven by the attraction of the Schiff base to a new counterion. 3D CP MAS experiments of NCOCX, NCACX, CONCA and CAN(CO)CA types have been used in studies of proteorhodopsin.71... 

A new total synthesis of flavopereirine perchlorate (148) has been reported by Ninomiya et al. (109) via enamide photocyclization. Harmalane (150) was acy-lated with 3-methoxyethacryloyl chloride to enamide 151 which was irradiated in benzene solution without purification to yield the unstable lactam 152. The latter was treated with hydrochloric acid, resulting in dehydrolactam 153 in a yield of 35% from harmalane (150). Lithium aluminum hydride reduction of 153, followed by dehydrogenation, afforded flavopereirine (148), isolated as its perchlorate (109). 

Stilbenes, photocyclization of, 30, 1 StiUe reaction, 50, 1 Stobbe condensation, 6, 1 Substitution reactions using organocopper reagents, 22, 2 41, 2 Sugars, synthesis by glycosylation with sulfoxides and sulfinates, 64, 2 Sulfide reduction of nitroarenes, 20, 4 Sulfonation of aromatic hydrocarbons and aryl halides, 3, 4 Swem oxidation, 39, 3 53, 1... 

Beccalli et al. reported a new synthesis of staurosporinone (293) from 3-cyano-3-(lH-indol-3-yl)-2-oxo propionic acid ethyl ester (1464) (790). The reaction of 1464 with ethyl chlorocarbonate and triethylamine afforded the compound 1465, which, on treatment with dimethylamine, led to the corresponding hydroxy derivative 1466. The triflate 1467 was prepared from 1466 by reaction with trifluoromethanesulfonic anhydride (Tf20) in the presence of ethyldiisopropylamine. The palladium(O)-catalyzed cross-coupling of the triflate 1467 with the 3-(tributylstannyl)indole 1468 afforded the vinylindole 1469 in 89% yield. Deprotection of both nitrogen atoms with sodium ethoxide in ethanol to 1470, followed by photocyclization in the presence of iodine as the oxidizing agent provided the indolocarbazole 1471. Finally, reductive cyclization of 1471 with sodium borohydride-cobaltous chloride led to staurosporinone (293) in 40% yield (790) (Scheme 5.248). 

Uang et al. reported a synthesis of staurosporinone (293) starting from arcyriarubin A (349). Oxidative photocyclization of bisindolylmaleimide 349 in the presence of a catalytic amount of iodine in THF/acetonitrile led to arcyriaflavin A (345) in 85% yield. Finally, using modified Clemmensen reduction conditions, arcyriaflavin A (345) was transformed to staurosporinone (293) in 68% yield (795) (Scheme 5.254). 

A novel and efficient synthesis of aporphinic alkaloids has been developed by Kupchan and O Brien (55) via oxidative photocyclization of l-(a-hydroxy-2-iodobenzyl)-6-hydroxy-7-methoxyisoquinolines such as 120, 121, or 122, all prepared by the Reissert method shown in Scheme 17. N-Methylation of oxo-aporphines 124 and 125 yielded corunnine (127) and nandazurine (128), respectively. Reduction of 124 with Zn-AcOH resulted in thalicmidine (130), and similar reduction of 125 gave domesticine (131) in racemic form. Caaverine (129) has also been prepared by this route (55). 

Acyl-2-phenyloxazole derivatives undergo a reductive photocyclization in the presence of sodium borohydride to generate a bicychc oxazoline with a cis-fused pyridinone ring 307. The stereochemistry of the product is consistent with hydride attack from the less hindered surface of the cyclic intermediate 306. The oxazoline containing pyridinone is a key intermediate used for the synthesis of pseudodisto-mins 308 (Scheme 8.85, p. 415). ° ... 

The intramolecular photoinduced electron transfer reaction of N-(o-chlorobenzyl)aniline 440 in the presence of sodium hydroxide in aqueous acetonitrile afforded, 9,10-dihydrophenanthridine and its dimer, which is reasonably explained by dechlorination from the radical anion of chlorobenzene chro-mophore followed by the cyclization (Scheme 130) [481], Similar photocyclization 9-(io-anilinoalkyl)-10-bromophenantherens 441 takes place to give spiro compounds, cyclized products, and reduction products dependent on the methylene chain length. The efficient intramolecular photocyclization occurs when the methylene tether is n = 3 [476] (Scheme 131). 

Anhydrolycorine (73) was prepared by photolytic dehydrobromina-tion of the amide 70, which gave the lactam 72 as first cyclization product. Reduction (LiAlH4) of 72 led to 73 in a good overall yield. Attempts to induce photocyclization of the amide 71 to 73, failed, the photo-Fries product 74 being the only relevant reaction result (9). 

A new synthetic approach to polycyclic aromatic compounds has been developed based on double Suzuki coupling of polycyclic aromatic hydrocarbon bis(boronic acid) derivatives with o-bromoaryl aldehydes to furnish aryl dialdehydes. These are then converted to larger polycyclic aromatic ring systems by either (a) conversion to diolefins by Wittig reaction followed by photocyclization, or (b) reductive cyclization with trifluoromethanesulfonic acid and 1,3-propanediol (Eq. (12)) [30]. 

Irradiation of the amide (54) gives the photocyclized product (55) which, on reduction and acetylation, affords45 thef product (56) containing the clavine ring... 

The photochemical reactions of some a-arylvinyl bromides (31), in acetic acid in the presence of sodium acetate and tetraethylammonium bromide (labeled with 8zBr) give nucleophilic substitution, reductive debromination, cis-stilbene photocyclization, and oxidation as the primary pathways to product... 

The course of the reductive photocyclization of enamines by irradiation in the presence of sodium borohydride depends on the nature of substituents. Thus the AT-methyl-S-phenyl compound 46 yields a mixture of the pyrrolidinone 47, the piperidinone 48 and the tricyclic compound 49, whereas the dimethyl analogue 50 gives the piperidinone 51 as a mixture of Z- and -isomers. The cyclopentene derivative 52 affords the spiro-pyrrolidinone 53, together with the cyclopentapiperidinone 54, the naphthylthio group being eliminated (Scheme 2)50. 

Reductive photocyclization of the enamide 261 by irradiating a methanolic solution containing sodium borohydride results in a mixture of four products the hexahydrophe-nanthridone 262, two geometrically isomeric octahydrophenanthridones, 263 and 264, and the structurally isomeric octahydrophenanthridone 265 (equation 111)135. 

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