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2-(Dideuteriomethylene)-1,1-bis(4-methoxyphenyl)cyclopropane (d[sub 2]-1) undergoes degenerate rearrangement in both singlet- and triplet-sensitized electron-transfer photoreactions. Nanosecond timeresolved absorption spectroscopy on laser flash photolysis of the unlabeled 1 with 9,10-dicyanoanthracene, 1,2,4,5-tetracyanobenzene, or N-methylquinolinium tetrafluoroborate as an electron-accepting photosensitizer gives rise to two transients with λ[sub max] at 500 and 350 nm assigned to the dianisyl-substituted largely twisted trimethylenemethane cation radical (6[sup •+]) and the corresponding diradical (6[sup ••] respectively. These intermediates are also detected, respectively, by steady state and nanosecond time-resolved EPR with chloranil or anthraquinone as a sensitizer. The degenerate rearrangement of d[sub 2]-1 thus proceeds via these two different types of intermediates in a cation radical cleavage-diradical cyclization mechanism. Energetics based on nanosecond time-resolved photoacoustic calorimetry support this mechanism. A comparison of the reactivities and the spectroscopic results of 1, 1,1-bis(4-methoxyphenyl)-2-methylenespiro[2.2]pentane (2), and 1-cyclopropylidene-2,2-bis(4-methoxyphenyl)cyclopropane (3) suggest that the reversible methylenecyclopropane rearrangement between 2 and 3 proceeds via a similar mechanism. [ABSTRACT FROM AUTHOR]

Synthesis of macrocyclic pentadecaphenylene was carried out via electron-transfer oxidation of the corresponding Lipshutz cuprate. Pentadecaphenylene self-aggregated in solution to form a gel. Furthermore, it incorporated C60 in its cavity to produce a fibrous inclusion complex which showed a high gelation ability in benzene. [ABSTRACT FROM AUTHOR]

The oxatetramethyleneethane (OTME) radical cation is a radical cation variant of an unprecedented oxa analogue of tetramethyleneethane. Expecting to generate OTME intermediate photoinduced electron-transfer reactions of 2,2-bis(p-methoxyphenyl)-3,3-dimethyl-4-methylenecyclobutanone and 2,2-bis(p-methoxyphenyl)-4-isopropylidenecyclobutanone is studied. The article reports a novel rearrangement of 1 to 2 together with electron paramagnetic resonance spectroscopy observations.

Abstract: Mechanistic studies and product analyses were performed on the single electron transfer (SET) promoted photoamination reaction between 2,5-dimethylhexa-2,4-diene (1) and 9-cyanophenanthrene in order to gain a comprehensive understanding of the effects of additive metal salts. The product selectivity of this process was found to be dramatically increased by the addition of Mg2+ salts. An investigation involving the analyses of fluorescence and time-resolved absorption spectroscopic properties reveals that Mg2+ enhances the rate of the initial SET step and stabilizes the resulting radical ion pair in this photoreaction. [Copyright &y& Elsevier]

Photochemical reactions of 2,5-bis[2,2-di(thien-2-yl)ethenyl]thiophene ( 1a ) and its tetramethyl derivative 1b , under direct photoexcitation, and photoinduced electron-transfer conditions, were studied. Our initial prediction was that 1b would undergo a photoreaction as part of a reversible photochromic system, while a reaction of its non-methyl substituted analog 1a would undergo a typical double sequence of 6π-electrocyclization (6π-EC)/aromatization (AR) (double dehydrogenation, 2H) to give 7,11-di(thien-2-yl)trithia[5]helicene ( 2a ). In fact, we observed that photoirradiation of 1b leads to formation of the 7,11-bis(3-methylthien-2-yl)trithia[5]helicene ( 2b ). In this process, 2b is formed via a double sequence of 6π-EC/AR (dehydrogenation/demethylation, H/ Me). Moreover, the yield of formation of 2b is much higher than that of 2a , which reacts through a double sequence of 6π-EC/AR ( 2H). Thus, this photochemically-induced paradoxical cascade reaction based on the newly uncovered reactivity serves as an efficient method to construct the trithia[5]helicene framework. [ABSTRACT FROM AUTHOR]

Abstract: Photoinduced electron-transfer reactions of several ketone substrates were studied to evaluate the utilities of 1,6-bis(dimethylamino)pyrene (BDMAP), 1,6-dimethoxypyrene (DMP), 9,10-bis(dimethylamino)anthracene (BDMAA), and 9,10-dimethoxyanthracene (DMA) as electron-donating sensitizers cooperating with 2-aryl-1,3-dimethylbenzimidazolines. BDMAP and DMP generally led higher conversion of ketones and better yield of reduction products compared to BDMAA and DMA. [Copyright &y& Elsevier]

Synthesis of macrocyclic pentadecaphenylene was carried out via electron-transfer oxidation of the corresponding Lipshutz cuprate. Pentadecaphenylene self-aggregated in solution to form a gel. Furthermore, it incorporated C60 in its cavity to produce a fibrous inclusion complex which showed a high gelation ability in benzene. [ABSTRACT FROM AUTHOR]