Cyclization photo

As we shall not be concerned directly with purely synthetic aspects of the photo-cyclization we would like to refer the interested reader to the comprehensive general reviews of Stermitz Blackburn and Timmons and to the yearly reviews of Gil-bert ... 

Diphenyl ethers with an ortho substituent may undergo a similar photo-cyclization to produce dibenzofurans by expulsion of the substituent from an intermediate 9b-substituted 9a,9b-dihydrodibenzofuran of the same type as 40. Thus the diphenyl ethers 43 and 44 on irradiation lose methanol with the production of the dibenzofurans 45 and 46 (Scheme 4). With less highly... 

Castle and co-workers <1996JHC119, 1996JHC185, 1997JHC1597, 1998JHC1441> used 3-chlorothieno [2,3-3]thiophene-2-carbonyl chloride 280 in the synthesis of the appropriate amides, which by oxidative photo-cyclization gave novel polycyclic heterocyclic ring systems thieno[3, 2 4,5]thieno[2,3-f][l,10]phenanthroline 281, thieno[3, 2 4,5]thieno[2,3-f]naphtho[2,iy ]quinoline 282 and thieno[3, 2 4,5]thieno[2,3-f]naphtho[l,2-g]qui-noline 283, thieno[3, 2 4,5]thieno[2,3-f]naphtho[l,2y ]quinoline 284, thieno[3, 2 4,5]thieno[2,3-f]naphtho[l,2 7]-[l,2,4]triazolo[3,4- ]quinoline 286, thieno[3, 2 4,5]thieno[2,3-f]naphtho[l,2-/]tetrazolo[l,5- ]quinoline 288, benzo[ ]thieno[3, 2 4,5]thieno[2,3-f]quinoline 285, benzo /]thieno[3, 2 4,5]thieno[2,3-f]quinoline 287, benzol/] thieno[3, 2 4,5]thieno[2,3-f]tetrazolo[l,5- ]quinoline 289, and benzo[/jthieno[3, 2 4,5]thieno[2.3-f][l,2,4]triazolo[4,3- ]-quinoline 290. 

A different type of indole ring synthesis was accomplished via an intramolecular cyclization of enaminoketones that proceeds through intermediate arylpalladium complexes (90H911). /3-Hydrocarbolines (33) were obtained as the final products. Similar results were obtained in the photo-cyclization of enaminoesters (91TL6129) and enaminolactones (95H1939). Results obtained in the cyclization of A-arylenamines to indoles with... 

Keywords 2-[A-(2-propenyl)amino]cyclohex-2-enone, inclusion complex, photo-cyclization... 

The biradical benzo-l,2 4,5-bis(l,3,2-dithiazolyl) (BBDTA) is known in the literature but characterization is incomplete. A new study reports the electronic, molecular, and solid-state structure of BBDTA.224 The lifetime of an alkyl phenylglyoxalate-derived 1,4-biradical has been estimated, using the cyclopropylmethyl radical clock , to be in the range 35—40 ns.225 The indanols (88) and their C(3) methyl and trideuteromethyl analogues have been prepared from phenyl benzyl ketone via photo-cyclization of an intermediate 1,5-biradical species.226,227 Selectivity for these products over their C(l) epimers is high but is profoundly effected by substitution in the benzyl ring or the alkyl side-chain. The findings are rationalized in terms of the conformational preference of the intermediate 1,5-biradicals. 

Lindemann, U., Reck, G., Wulff-Molder, D., and Wessig, P. (1998) Photo-cyclization of 4-oxo-4-phenyl-butanoyl amines to 8-lactams. Tetrahedron,... 

The spirocyclic CD-ring of 197, the precursor of the harringtonine family of alkaloid 198, is constructed efficiently (33% yield) by allyliminium salt 196 photo-cyclizations [88], as shown in Scheme 8.54. 

Meador, M.A. and Wagner, P.J. (1983) 2-Indanol formation from photo-cyclization of a-arylacetophenones. Journal of the- American Chemical Society, 105, 4484-4486. 

The key step in the synthesis of the azaphenanthrene alkaloid eupoulauramine 27 (56% yield) is an intramolecular SRN1 reaction, followed by in situ stilbene photo-cyclization, and further methylation (Scheme 10.52) [68]. 

There are four distinct processes initiated by y-hydrogen abstraction in excited carbonyl compounds Norrish type II photoelimination, Yang photo-cyclization (cyclobutanol formation), Yang photoenolization (o-xylylenol formation), and (3-cleavage of radicals from carbons adjacent to the radical sites of the 1,4-biradicals. Some of these require unique structures and generate distinct products. 

Stilbene is well known to undergo a trans-cis photoisomerization upon irradiation with UV light.1 In addition to this isomerization, stilbene shows a photo-cyclization reaction to produce dihydrophenanthrene. 

The host-guest and ionic chiral auxiliary approaches have been most intensively applied for solid-state asymmetric induction. A number of achiral organic compounds could be converted into chiral compounds in high enantioselectivities. However, all the photoreactions in themselves are well-known intramolecular photoreactions photocyclization, [2 + 2] photocyclization, Norrish type II photo-cyclization, di-ir-methane photorearrangement and photoisomerization. New types of asymmetric photoreactions have never been reported. 

Giese and co-workers reported the asymmetric photo-cyclization of 93 via short-lived diradical intermediate P in the presence of a triplet quencher, naphthalene. Because of the extremely fast cyclization of the singlet diradical P, racemization through bond rotation was minimized.45... 

Dicentrine and Dicentrinone. Dicentrine (283) was synthesized by photo-cyclization of the o-bromo- and chloroenamides 282a and b by Cava et al. (138) the former enamide (282a) was best suited for the synthesis of the alkaloids in view of yield and reaction time (Scheme 103). 

The central macrocyclic rings of vitamin [148] and other similar natural products [149] have been constructed by using unique methodologies, e.g. electrochemical oxidation. As a special example of macrocyclization, here photo-cyclization is discussed. Battersby and coworkers [149 b] efficiently synthesized sirohydrochlorin (249), an isobacteriochlorin isolated as the metal-free prosthetic group of sulphite reductase. Photochemical treatment of the seco precursor 247 for 3 to 4 days yielded 24S which was hydrolyzed to 249 (Scheme 83). 

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