Arene olefination

The literature of diene and polyene photochemistry provides many cases of synthetically useful reactions. As a result, certain arbitrary decisions have been made regarding what is covered in this chapter. For example, intramolecular [2 + 2]-photocycloaddition reactions of a, >-dienes can be formally included under the general rubric of diene photochemistry. However, we have chosen to restrict our discussion to dienes and polyenes which constitute a self-contained chromophore, viz. conjugated, cross-conjugated and 1,4-diene systems. Likewise, arene-olefin photocycloadditions will not be considered. These two broad classes of photoreactions have been applied extensively in synthesis, and have been the subject of recent reviews3,4. 

The intramolecular [5 + 2] cycloaddition mode has been studied extensively. The chemistry bears a remarkable similarity to the arene-olefin meta-photocycloaddition [53] reaction (e.g. 114... 

Making elegant use of the intramolecular arene-olefin meta-cycloaddition reaction, Wender and Howbert have achieved a total synthesis of ( + )-cedrene (575) Irradiation of 569 led to an approximately equal mixture of 570 and 571 which... 

Arene-Olefin Photocyclization Organic Photochemistry 1989, 10,357 - the photochemistry of benzene is dominated by the singlet state... 

Wender PA, DeLong MA. Synthetic studies on arene-olefin cycloadditions. XII. Total synthesis of ( )-subergorgic acid. Tetrahedron Lett 1990 31(38) 5429-5432. 

Scheme 34 Bimolecular deactivation of the arene olefin. (From Ref. 182.)...

A schematic representation of the possible processes in arene-olefin photocycloaddition according to Leismann et al. [182] is given in Scheme 35. Increasing charge separation in the exciplex, caused by decreasing ionization potentials of the olefins, can lead to zwitterionic intermediates, which are able to form ortho adducts. Increasing solvent polarity can reduce the formation of adducts by propagating the formation of radical ion pairs. The possibility that the ortho adduct may be formed directly or via a different short-lived intermediate was not incorporated in the scheme. 

Scheme 35 Formation of the arene-olefin (Ar-Ol) exciplex and its deactivation by charge-transfer effects induced by changes of olefin ionization potential (IP) and solvent polarity according to Leismann et al. (From Ref. 182.)...

Guo, X.-C. and Chen, Q.-Y. (1999) Photo-induced intramolecular arene-olefin meta-cycloaddition of 5-phenyl-fluorinated-pent-l-enes. Journal of Fluorine Chemistry, 97 (1—2), 149-156. 

Yamamura has extensively explored the intramolecular [5 - - 2]-cycloaddition mode. This chemistry bears a remarkable similarity to the so-called arene olefin meta-photocycloaddition [64] reaction (e.g., 267 to 268) that has frequently been used in the synthesis of complex bioactive natural products. While different intermediates are involved, the photo-and electrochemical reactions provide access to many of the same basic ring systems. This is nicely demonstrated by comparing key steps and the outcome of an electrochemical approach to the total synthesis of pentalene (53) [65] and a photochemical pathway that ultimately led to cedrene (compare equations 48 and 49). 

Nuss, J.M., Chinn, J.P., and Murphy, M.M., Substituent control of excited state reactivity. The intramolecular ortho arene-olefin photocycloaddition, 7. Am. Chem. Soc., 117, 6801, 1995. 

Nuss, J. M., Chinn, J. P., Murphy, M. M., Substituent Control of Excited state Reactivity. The Intramolecular ortho Arene Olefin Photocycloaddition, J. Am. Chem. Soc. 1995, 117, 6801 6802. 

The arene-olefin cycloaddition has been used in a synthesis of the... 

The first step of this reaction is the palladation of the arene. Olefin insertion into the Ar-Pd bond is then possible [12] ... 

The 1980s witnessed a revival of interest in synthetic photochemistry, largely based on the successful application of intramolecular arene-olefin and enone-olefin photochemical cycloaddition reactions to the synthesis of polycyclic natural and unnatural products. The potential application of intramolecular arene-amine addition to the synthesis of alkaloids was suggested in 1973 by Btyce-Smith et al.," based on their observation of intramolecular photochemical 1,4-addition reaction of the (N,A/-dimethylaminoalkyl)benzenes I and 2 to yield 3 and 4, respectively. Intramolecular addition reactions have subsequently been observed for a large number of (aminoal-... 

The arene-olefin cycloaddition reaction has now been applied to... 

The arene-olefin meta-photocycloaddition approach to triquinane natural products is further illustrated this year with a three-step total synthesis of ( )-silphinene (5) starting from 2-bromotoluene (1). Thus, irradiation of the arene-olefin (2) derived from (1) gave a 1 1 mixture of the photoadducts (3) and (4) in 70% yield. Regioselective reductive cleavage of the cyclopropane bond in (3),... 

RuHCl( -C6Me )(PPh3)] Arenes, olefins Alkanes H2 5 MPa, 323 K... 

Olefination via Pd(II) C—H functionalization is not limited to carbon-based arenes. Olefination of the C-2 position of pyridines can be accomplished through the A-oxide. Intra-molecular-directed alkenylation of pyridines leading to... 

Ligand exchange reactions involving arenes, olefins, and acetylenes occur. Give examples of all their exchange reactions. 

A fascinating new route to ( )-hirsutene involves an arene-olefin photocycloaddition of the acetate (105) to form the alcohol (106), albeit in low yield, as a mixture of three isomers. Acid-induced cleavage of a cyclopropane ring then... 

Wender PA, Singh SK (1990) Synthetic Studies on Arene-olefine Cycloaddition. 11. Total Synthesis of (-)-Retigeranic Acid. Tetrahedron Letters 31 2517... 

Iwata, C., Takemoto, Y, Doi, M., and Imanishi, T. (1988) Stereoselective total synthesis of ( )- subergorgic add, a new type of angular triquinane sesquiterpene. /. Org. Chem., 53,1623-1628. Wender, P.A. and DeLong, M.A. (1990) Synthetic studies on arene-olefin cycloadditions. XII. Total synthesis of ( )-subergorgic acid. Tetrahedron Lett., 31, 5429-5432. 

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