Substituent effects on the photorearrangements of unsymmetrically substituted diazinobarrelenes
A series of diazinobarrelenes 8-15 engendered with alkyl functionalities at the barrelene skeleton were irradiated with 350 nm light under direct and acetone-sensitized reaction conditions. Under these conditions, all the barrelenes except barrelene 14 afforded semibullvalenes with varying degrees of regioselectivity and product distribution. Dicyanopyrazinobarrelenes 8-10 which furnished semibullvalenes 32-41via the aryl-vinyl initial bridging route were strongly controlled by the nitrile functionalities installed at the aromatic sites. Benzoquinoxalinobarrelenes 11-13 which afforded semibullvalenes 42-49, preferentially underwent photorearrangement via vinyl-vinyl bridging even if the compounds were excited at a wavelength where the quinoxaline moiety absorbed most of the light. Zimmerman's bridging hypothesis and the possibility for quinoxalines to undergo intramolecular triplet energy transfer could reasonably account for the observed regioselectivity. Barrelene 14 was insensitive to photorearrangement whereas benzo[f,h]quinoxalinobarrelene 15 preferentially underwent ADPM rearrangement affording semibullvalenes 50-52. Electronic and steric factors of alkyl substituents overwhelmingly controlled the product forming steps whereas localization and minimization of triplet energies greatly influenced the initial bridging interaction. The Royal Society of Chemistry 2013.
Hsieh, Hsing-Pang,Chen, Ann-Cheng,Villarante, Nelson R.,Chuang, Gary J.,Liao, Chun-Chen
p. 1165 - 1178
(2013/03/14)
Regioselective synthesis of novel heterophanes from 4-amino-triazoles
The regioselective synthesis of N-amino-benztriazolophanes has been achieved by incorporation of benzene nucleus in the heterophane. The some of the novel compounds have been studied for their use as PTC agents.
Chande, Madhukar S.,Athalye, Shailesh S.,Godbole, Ajit A.
p. 670 - 673
(2007/10/03)
Synthesis and structural studies of novel 1,3,4-oxadiazolophanes
The title compounds have been prepared in moderate yields from compound 2a/2b as starting unit, which are obtained, in good yields by one-step process in high purity. Interesting results have been obtained when the cyclisation products were studied for structural analysis. The title compounds are also studied for their use as PTC agents.
COMPETITIVE REARRANGEMENTS. I. NEOPENTYLIC VERSUS SKELETAL BICYCLOOCTANE -> BICYCLOOCTANE REARRANGEMENTS
Generation of a carbenium ion common to two systems which are able to undergo either a skeletal bicyclooctane --> bicyclooctane rearrangement or a neopentylic rearrangement conducts only to the latter reaction. Thus, 8-carbomethoxy-7-t-butyl-dibenzobicyclooctatriene (15) reacts with strong acids or bromine, yielding neopentyl rearranged products 17, respectively 21. Reaction mechanisms are proposed.
Ionica, Ileana,Ghiviriga, Ion,Filip, Petru,Badea, Florin,Dinulescu, Ilie G.