Photocyclo

In recent years the application of photocycloaddition reactions to organic synthesis has been growing in importance. The procedure described is illustrative of a general method based on a photocyclo-additibn reaction for the introduction of an activated alkyl group specifically to the a-carbon atom of an a,jS-unsaturated cyclohexenone. Especially significant is the fact that the method is also applicable to... 

We have found a rare reaction where two topochemical processes occur competitively in a single crystal, that is, a competitive photocyclo-dimerization and -polymerization in the crystal of 1,4-dicinnamoylbenzene 3 (15). On photoirradiation with a mercury lamp (100W) at 20°C for 9 h, the crystals of 3 (2.00g), dispersed in heptane (400 ml), are transformed into amorphous substances consisting of a tricyclic dimer, 21,22,23,24-tetraphenyl-1,4,11,14-tetraoxo-2 (3), 12 (13) -diethano(4,4Jparacyclophane, 4 (isolated yield 57%) (16), a mixture of oligomers (ca. 30%) and unreacted 3 (7%). 

Keywords acenaphdiylene, tetracyanoethylene, CT complex, [2+2]photocyclo-addition, cyclobutane... 

Photodimerization of anthracene has frequently been cited as a photochemical switch to create photoresponsive crown ethers. Photoirradiation of 3 in the presence of Li+ gives the photocyclo-isomer 4 [5,6], 4 is fairly stable with Li+ but readily reverts to the open form 3 when Li+ is removed from the ring. In this system, however, intermolecular dimerization may take place competitively... 

Buu Hue, B.T., Dijkink, J., Kuiper, S.v., Schaik, S.v., Maarseveen, J.H., and Hiemstra, H. (2006) Synthesis of the tricyclic core of solanoeclepin a through intramolecular [2 + 2] photocyclo-addition of an allene butenolide. European Journal of Organic Chemistry, 127-137. 

Regio- and stereochemistry of Paterno-Buchi photocyclo additions of carbonyl compounds and cyclic vinyl ethers leading to formation of oxetanes 04ACR919. 

The photochemistry of diphenyltriafulvenes is complicated by the rearrangement of initially produced dimers. With (322 = CN = CN or COjMe), photocyclo-... 

Tlie second example of such an asymmetric synthesis involves a (2+2)-photocyclo-addition reaction in a two-component single crystal. A mixed crystal of the diphenyl-butadiene shown in Scheme 5 with its thiophene analog was irradiated with light absorbed only by the latter. One of the enantiomeric heterodimers was produced in excess [8]. 

Winkler, J.D., Siegel, M.G., and Stelmach, (,E, (1993) A highly stereoselective approach to the synthesis of the manzamine alkaloids via the intramolecular vinylogous amide photocyclo-addition. Tetrahedron Lett., 34, 6509-6512,... 

Ghosh, S., Patra, D., and Samajdar, S., Intramolecular [2 +2 ]-photocyclo-addition-cyclobutane rearrangement. A novel stereocontrolled approach to highly substituted cyclopentanones. Tetrahedron Lett., 37, 2073, 1996. 

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