Photocycloaddition of S,S-Dioxo-benzothiophene-2-methanol, Reactivity in the Solid State and in Solution: Mechanistic Studies and Diastereoselective Formation of Cyclobutyl Rings (original) (raw)
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Journal of Photochemistry and Photobiology A-chemistry, 2002
r-1,c-2,t-3,t-4-1,3-di(4-R-phenyl)-2,4-bis[2-(5-phenyloxazolyl)]cyclobutane (IIa: R = H; IIb: R = Cl; IIc: R = OMe; IId: R = t-Bu) was synthesized with high stereo-selectivity via the photodimerization of its corresponding trans-monomer in hydrochloric acid. The structures of the title compounds were identified by elementary analyses, IR, UV, 1 H NMR, 13 C NMR and MS. It has been proved that the photodimers have syn-head-to-tail configuration. The investigation revealed that under irradiation of 254 nm UV light, these photodimers underwent photolysis promptly to reproduce the trans-monomers and then the formed trans-monomers transformed into their cis-isomers by trans-cis isomerization.
Crystal Growth & Design, 2018
Solid state [2 + 2] cycloaddition photochemical reactions have recently emerged as a benign green method to synthesize cyclobutane derivatives. Synthesis of cyclobutane isomers are often controlled by the manner in which unsymmetrical olefin pairs have been aligned either in a head-to-head (HH) or head-to-tail (HT) manner using bridging ligands, organic templating agents, metalorganic clipping agents, and metallophilic interactions. Here we synthesized three Zn(II) one-dimensional coordination polymers (1D CPs) in which the terminal ligands having olefin groups are aligned in both a HH and HT fashion to undergo a photo-cycloaddition reaction. Of these, two CPs provided HH photoproducts, while the third CP gave a mixture of HH and HT photoproducts. These results hope to provide additional knowledge to design the solids to obtain the desired cyclobutane regioselectively.
Journal of the American Chemical Society, 1971
Mechanistic studies on the photorearrangements of benzobicyclo[2.2.2]octadienone (1) and bicyclo-[2.2.2]octenone (5) are reported. The limiting quantum yields for the singlet reaction of 1 are: &is = 0.50; @nsphthslene = 0.45; ~4,5-benLobie,c~o[l.l.0100ta-2,1-dion.8~0~~ = 0.10. The limiting quantum yields for the acetophenonesensitized reaction are: adis = 0.14; anaphthslene = 0.01 ; ~b e n r o t r i o y e l o [ 3 . 3 . 0 , 0 2~8~~~t e n~3 . 0 n e = 0.12. A deuterium labeling experiment established the 1,2-acyl migration mechanism for the photosensitized rearrangement of 1. Finally, it was shown that the triplet reaction proceeded by a concerted, symmetry-allowed process by comparison with the photoisomerization of lactone 12.
Journal of The Chemical Society-perkin Transactions 1, 1992
The photochemistry of 4-phenoxybut-1 -ene is markedly influenced by the presence and position of electron-withdrawing substituents on the benzene ring. A cyano substituent in the 2'-or 4'-position promotes an efficient intramolecular cycloaddition to give good yields of the 4-oxatricyclo-[7.2.0.03*7] undeca-2,lO-dienes, by way of the photolabile 1 1 -oxabicyclo[6.3.0] undeca-l,3,5-triene, the precursor of which is presumed to be a thermally labile intramolecular ortho photocycloadduct. The 3'-cyano isomer reacts inefficiently and only the 2'-isomer in the methoxycarbonyl series undergoes the photocycloaddition. The formation of the trienes is efficiently quenched by 1,3-dienes but their intramolecular cyclisation is unaffected by the presence of the triplet quenches.
Journal of the American Chemical Society, 1980
The photochemical reactions of several 3-allyl substituted diphenylcyclopropenes have been studied. Irradiation of 2-methyl-3-( l-methyl-2,3-diphenyI-2-cyclopropen-1 -yl)-I-propene produced products derived from both cyclopropenyl ring opening and side-chain fragmentation. The formation of a bicyclo[3.1 .O]hex-2-ene from the irradiation can be rationalized in terms of a vinylcarbene intermediate which undergoes internal cycloaddition. Successive introduction of methyl groups on the (Y or y carbon of the allyl side chain was found to dramatically increase the importance of side-chain cleavage relative to ring opening. Thus, irradiation of the 3-prenyl substituted system was found to give rearranged products corresponding to a 1,2-substituent shift. The results obtained from our studies reveal the following trends: ( I ) excited cyclopropene singlets give products consistent with ring cleavage or side-chain fragmentation, whereas triplet states undergo intramolecular [2 + 21 cycloaddition; (2) the 1,2-substituent shift only occurs with 1,2-diphenyl substituted cyclopropenes; (3) the rearrangement is completely regiospecific leading to unsymmetrically substituted cyclopropenes; (4) side-chain fragmentation competes with ring opening as a primary process when stable radicals are produced. A mechanism involving a dissociation-reassociation process is proposed to account for the formation of the rearranged cyclopropenes.
Two Carbon Ring Expansion by Photochemical Ring Opening of Electrophilic Cyclobutenes
Tetrahedron Letters, 1997
The photolysisof clectrophiliccyclobutencs condensed to a diquimmicmoietyand bearing eitherass aminogroupor a hydroxylgroupat dscringjunctionleadsto thecorresponding hydroazulenic derivativesin highyields. O 1997 Elsevier ScienceLtd. The bicyclo [5.3.0] decwre (or hydroazulene) skeleton is found in a wide range of natural productsl. Among the numerous synthetic pathways developed for their synthesis, the two carbon ring enlargementvia cyclobutane derivatives (e. g. tricyclodecane-+ hydroazulene) proved to be a very useful method2. The two carbon ring expansion via electrophilic cyclobutenes is, on the contrary, seldom used3.
Supramolecular photochemical synthesis of an unsymmetrical cyclobutane
Photochemical & Photobiological Sciences, 2007
2-Styrylbenzothiazole (1) and cinnamic acid (2) derivatives containing 15-crown-5 ether moieties form a supramolecular assembly in the presence of Ba 2+ cations in acetonitrile. The assembly is stabilized by hydrogen bonding between the heterocyclic N atom of 1 and the proton of the carboxylic group of 2, by sandwich Ba 2+ complex formation between the crown ether moieties of 1 and 2, and by p-p stacking interactions. Irradiation of solutions containing these supramolecular complexes leads to highly specific formation of an unsymmetrical cycloadduct. This investigation provides an interesting example of supramolecular control of [2 + 2]-photocyclization in solution.