Photocycloaddition styrene deriv

In 1987, Nishimura, one of the authors, and his co-workers discovered that the [2 -t- 2] photocycloaddition of styrene derivatives proceeds smoothly, when pertinent conditions are carefully chosen. By this method, many cyclophanes including orthocyclophanes, metacyclophanes, paracyclophanes, (4,4 )-biphenylophanes, (1,4)-, (1,5)-, and (2,6)naphthalenophanes, (1,6)- and... 

In 1986, it was recognized for the first time that the [2 -I- 2] photocycloaddition of styrene moieties was efficient if proper conditions were chosen." After this discovery, many simple phanes were prepared from styrene derivatives or from vinylarenes by using the [2 -I- 2] photocycloaddition in solution. This photochemical approach to cyclophanes is reviewed in this chapter, which focuses on the scope and limitations of the process. 

Inokuma, S., Yamamoto, T., and Nishimura, J., Efficient intramolecular [2-1-2] photocycloaddition of styrene derivatives toward new crown ethers. Tetrahedron Lett., 31, 97, 1990. 

Styrene derivatives are commonly used addends in the photocycloaddition studies of 1,4-quinones. With Z- and -anethole, 1,4-benzoquinone (BQ), 1,4-naphthoquinone (NQ), and 9,10-anthraquinone in acetonitrile solvent yield spiro-oxetanes in which the trans-isomer (e.g., 4 from naphthoquinone) predominates. The process has been studied in detail by CIDNP techniques from which it is deduced that product formation proceeds from triplet radical ion pairs to the triplet biradical, and that there is no significant contribution from direct conversion of exciplex intermediates into the biradicals. Spiro-oxetane formation between simple alkenes and BQ generally has low regioselectivity but this is markedly improved with alkylidene cyclohexanes (Figure 87.3) such that the major isomer can be used as a new access to useful synthetic building blocks. For the BQ/homobenzvalene 5 system, however, where the difference in stability between the intermediate biradicals can be expected to be considerably less, the selectivity ratio for the spiro-oxetanes 6 and 7 is reduced to 3 1, respectively, and the addition to NQ yields only the cyclobutane derivative 8. Quadricyclane and norbornadiene undergo the same photocycloaddition reaction to BQ, affording the oxolane 9 and the spiro-oxetane 10. Evidence from CIDNP... 

Another illustration of the role of the conformational mobility on the level of the observed asymmetric induction is shown by the intramolecular photocycloaddition of cinnamyl derivatives of vinyl glycine 73 into a mixture of 74 and 75 (Scheme 17). In the sensitized reaction and for steric reasons, the attack of -77,-77 excited styrene on the vinyl oxazolidinone 76 gives mainly 77 [55]. 

Although [2+2] photocycloaddition is not limited to reactions of olefins with enone derivatives (styrene and other aromatic alkenes can also undergo this type of photoreaction [11]), the majority of the recent literature has focused on the enone systems, and this will make up the bulk of our discussion. 

Sugimura et al. have also used tethers comprising chiral 2,4-pentanediol derivatives (127) to control the intramolecular photocycloaddition of a styrene unit to... 

Photocycloaddition of 2-methyl- and 2-ethyl-naphthoquinone to styrene yields three cyclobutane products (457,458) in which the 8-phenylisomer dominated. " The ratio of 7-phenyl to 8-phenyl products was 1 6 for the methylquinone and 1 3.5 for the ethyl derivative. The authors suggest that in these examples dipole-dipole interactions overcome any adverse repulsions. Changes in the olefin brings about changes in the ratio of products. Thus with 2-phenylpropene the ratio... 

The photocycloaddition of 2tf-azirines to electron-deficient olefins produces d -pyrrolines as primary photoproducts. Some of the dipolarophiles used include acrylic esters, acrylonitriles, fumaric and maleic esters, methyl allenecarboxylate, norbornene, and l,2-dicyanocyclobutene. Similarly, styrenes and vinylpyridines undergo smooth photocycloaddition to 2H-azirines. Addition of acetylene derivatives to the transient nitrile ylide gives 2H-pyrroles (18, 20) which rearrange to pyrroles (19) if the C-2 atom is monosubstituted. 3-Phenyl-2/f-azirines have been found to cycloadd to vinylphosphonium salts and to vinyl sulfones. The initial adducts (22 and 24) undergo ready loss of the phosphorous or sulfur substituent to give 2H-pyrroles (23 and 25). ... 

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