Cheruvallil S. Rajesh

Formal dipolar cycloaddition of allylsilanes to o-quinonoid compounds: a convenient route to benzofused and spirofused heterocycles ☆

Formal dipolar cycloaddition of allylsilanes to o-benzoquinones proceeds in a [2+3] manner affording dihydrobenzofurans. With isatins [3+2] annulation of the keto carbonyl occurs yielding spiro-oxindole derivatives.

Photoelectron transfer induced decarboxylation of substituted carboxylic acids across a liquid/liquid interface

Abstract Methylene blue photocatalyzed electron transfer reactions of some phenoxyacetic acid derivatives and N-phenylglycine across a liquid/liquid interface led to their efficient decarboxylation. Nanosecond laser flash photolysis studies of this process, in a reverse micellar system of Aerosol-OT (AOT)-benzene-water indicated that the liquid/liquid interface acts as a barrier in controlling the energy wasting back electron transfer. Intramolecular CC bond forming reactions of these radicals were utilized for the synthesis of various chroman derivatives.

Photochemical electron transfer across a liquid/liquid interface: Methylene Blue-sensitized decarboxylation of substituted carboxylic acids

Abstract Methylene Blue photocatalyzed electron transfer reactions of some substituted carboxylic acids across the water/benzene interface lead to efficient decarboxylation of these acids and the utility of this procedure has been demonstrated by the synthesis of some dihydrobenzopyran and dihydrobenzofuran derivatives.

Optical spectroscopic studies of mononitrated benzo[a]pyrenes.

Spectroscopic properties, including absorption, emission spectra, and excited-state lifetimes of the mononitrated benzo[a]pyrenes (NBaPs), specifically 1-, 3-, and 6-nitrobenzo[a]pyrenes (1-, 3-, and 6-NBaP), are reported, and correlations with structure are developed. With 1- and 3-NBaP, bathochromic shifts are observed in the absorption spectra. The quantum yields of emission display the following trend: BaP >> 6-NBaP > 1-NBaP approximately 3-NBaP. Fluorescence lifetimes for nitrated BaPs were approximately 6 to 7 times shorter than that of BaP. With the help of time-dependent density functional theory (TD-DFT), assignments of the electronic transitions are proposed and are in good agreement with the electronic spectra for the NBaPs in methanol. On the basis of optimization of the triplet states, different photochemical consequences are discussed, and the observed fluorescence quenching is explained. Changes in the electron density distributions in the ground and excited states calculated at the second-order coupled-cluster level using the resolution-of-the-identity approximation (RI-CC2) provide information about the possible mechanism of photochemical reactions of NBaPs. Correlations between the orientation of the nitro group relative to the aromatic plane and the observed properties of the NBaP are discussed.

Dipolar cycloaddition of carbonyl ylides to para-quinoneimides: a facile route to bicyclo[3.2.1] and [2.2.1] systems☆

Five- and six-membered carbonyl ylides formed from rhodium carbenoids add to p-quininoneimides to afford bicyclic compounds in good yields.

Photorearrangements of bridgehead-disubstituted dibenzobarrelene esters and lactones☆

Abstract This study deals with the photorearrangements of a few bridgehead-disubstituted dibenzobarrelene, i.e. dimethyl-9-hydroxymethyl-10-methyl-9,10-dihydro-9,10-ethenoanthracene-11,12-dicarboxylate (1) and the dibenzobarrelene lactone derivatives (10a,b). Irradiation of 1 in benzene gives a 77% yield of a dibenzocyclooctatetraene (8) with C2 symmetry with respect to its substituents. In contrast, the photolysis of 10a yields the dibenzosemibullvalene (15a) in nearly quantitative yield. Similarly, the dibenzobarrelene lactone (10b) undergoes facile photoisomerization to the corresponding dibenzosemibullvalene (15b) in 92% yield. The structures of the photoproducts 8 and 15a have been unambiguously established through X-ray crystallographic analysis.

Photochemistry of triethylamine-acid chloride charge-transfer complexes

Charge-transfer (CT) complexes formed between various para-substituted benzoyl chlorides and triethylamine in acetonitrile have been studied spectrophotometrically. Photoactivation of these CT complexes lead to products arising from the reactions of acyl and aminoalkyl radicals. These photochemical processes have been utilized to generate acyl radicals from O-allylsalicylyl chloride which undergoes intramolecular cyclization to form 3-methylchroman-4-one 20 in good yields.

Transient absorption studies on 3,6-dibromo polyvinylcarbazole and its model compounds

3,6-Dibromo-N-ethylcarbazole (DBNEC) and its polymeric analogue poly-3,6-dibromovinylcarbazole (PDBVCz) were studied by transient absorption spectroscopy. The transient absorption spectrum of the 3,6-dibromo-N-ethylcarbazole radical cation and decay rate constants of radical cations of 3,6-dibromo-N-ethylcarbazole and its polymeric analogue are presented. In the case of unsubstituted carbazole, the ratio of the yield of radical cation of monomer to polymer is 2.0, whereas in the case of PDBVCz, under the same experimental conditions, the yield of the radical cation is an order of magnitude less in comparison with the monomer model compound DBNEC. This drastic difference in yield has been correlated to the difference in the conformational structure of the polymer as evidenced by nuclear magnetic resonance spectroscopy.

Corrigendum to “Dipolar cycloaddition of carbonyl ylides to para-quinoneimides: a facile route to bicyclo[3.2.1] and [2.2.1] systems”: [Tetrahedron Letters 42 (2001) 2045–2046]

The authors regret that an error occurred in the assignment of the stereochemistry for the products 3a and 5(a–c) in Figure 1 and Schemes 1 and 3. The correct assignments are shown below.