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Université de Fribourg

Photochemistry of allenyl salicylaldehydes

Birbaum, Frédéric ; Neels, Antonia ; Bochet, Christian G.

In: Organic Letters, 2008, vol. 10, no. 15, p. 3175–3178

The intramolecular photocycloaddition of aryl aldehydes containing allene side chains is a versatile reaction as it provides a rapid and efficient access to original complex structures such as 1,3,4-tetrahydro-1,4-epoxy-5-alkylidene-2-benzoxepines 2 and substituted 2-oxa-tricyclo[5.2.2.0]1,5undeca-4,8,10-triene-9-carbaldehydes 3. Novel polycyclic structures are...

Université de Fribourg

New safety-catch photolabile protecting group

Riguet, Emmanuel ; Bochet, Christian G.

In: Organic Letters, 2007, vol. 9, no. 26, p. 5453 -5456

Photolabile protecting groups have proven their usefulness on many occasions. Their versions as linkers are however less attractive, as robustness and real orthogonality become critical issues. Safety-catch systems, where a preliminary activation phase is necessary, circumvent the problem of premature cleavage. In this work, we introduce a new safety-catch photolabile protecting group, whose...

Université de Fribourg

Isotope effects in photochemistry: application to chromatic orthogonality

Blanc, Aurélien ; Bochet, Christian G.

In: Organic Letters, 2007, vol. 9, no. 14, p. 2649-2651

The main challenge in developing new wavelength-specific photolabile protecting groups is the rigorous control of the photolysis rate. This rate is controlled by two factors: the chromophore absorbance and the reaction quantum yield. Fine-tuning the properties by changing substituents or structural features is difficult, because both factors are independently affected. By the use of the kinetic...

Université de Fribourg

Photoacylation of alcohols in neutral medium

Débieux, Jean-Luc ; Cosandey, Anne ; Helgen, Céline ; Bochet, Christian G.

In: European Journal of Organic Chemistry, 2007, p. 2073 - 2077

We report here conditions which allow the photoacylation of primary, secondary and tertiary alcohols with N-acetyl-5,7-dinitroindoline under exceptionally mild conditions, at wavelengths harmless to most functional groups, including otherwise photosensitive ones.

Université de Fribourg

Photochemical release of various functional groups

Bochet, Christian G.

In: Pure and Applied Chemistry, 2006, vol. 78, no. 2, p. 241-247

The photochemical liberation of functional groups is an attractive alternative to the traditional chemical approach. Several photolabile protecting groups have been developed in the past decades, but they were mainly designed to protect amines and carboxylic acids. In this account, we present some of our recent work on the photochemical release of other functions, such as silanols, aldehydes,...

Université de Fribourg

Hydrogen bond stabilization in Diels–Alder transition states: The cycloaddition of hydroxy-ortho-quinodimethane with fumaric acid and dimethylfumarate

Tamilmani, Venkatachalam ; Daul, Claude A. ; Lage Robles, Jaime ; Bochet, Christian G. ; Venuvanalingam, P.

In: Chemical Physics Letters, 2005, vol. 406, no. 4, p. 355-359

DFT investigations on the mechanism of Diels–Alder reactions of a hydroxy-ortho-quinodimethane with fumaric acid derivatives were performed to understand the origin of the syn or anti configuration of the adducts. The diene hydroxyl group and the dieneophile carboxyl group show hydrogen bonding in the transition state, significantly favouring the syn product. This reaction is poorly...

Université de Fribourg

Chromatic Orthogonality in Organic Synthesis

Bochet, Christian G.

In: Synlett, 2004, no. 13, p. 2268-2274

A major challenge in organic synthesis is the selective reaction of a functional group in the presence of others. This can be achieved by using an appropriate reagent, tuned to react exclusively at the desired center. An alternate approach would be to use a single reagent, and to transmit from the outside the information as to where it should react. This account describes the use of light as a...

Université de Fribourg

Geometry determination of tetrasubstituted stilbenes by proton NMR spectroscopy

Fluxá, Viviana S. ; Jenny, Titus A. ; Bochet, Christian G.

In: Tetrahedron Letters, 2005, vol. 46(2), p. 3793-3795

A simple spectroscopic method was applied to determine the geometry of tetrasubstituted alkenes. The observation of the ⁵J-coupling constants in proton NMR spectra on the ¹³C satellite signals could confirm the previous misassignment of 2,3-diphenylbutene. Hence, the (E)-isomer showed a 1.5 Hz coupling constant, whereas the (Z)-isomer showed a 1.1 Hz coupling constant. Based on this new...