The unexpected ability of arylzinc reagents bearing electron-donating substituents to react in a Friedel-Crafts fashion (cine) with electrophiles like perpivaloylated glucoside bromide and benzhydryl bromides in competition with organometallic coupling (ipso) is shown. The stereoelectronic factors required to promote the cine reactivity versus the classical ipso, and the mechanism of this alternative pathway, have been investigated. The Wheland intermediate is deprotonated intramolecularly in a 1,2-shift but also in a longer-range shift, leaving in this case the C-Zn untouched. In the latter case, it is possible to take advantage of this result for further functionalization.

International audienceOriginal basic or acidic organic compounds derived from guanidine or phenyl phosphonic acid were specifically designed and tested as new catalysts for the bulk synthesis of polyurethane prepolymers from a precursor system with particularly low reactivity (secondary alcohol + aliphatic isocyanate at low temperature). Both families showed interesting catalytic activities at 60-80 degrees C, but must nevertheless be used in much higher amounts (1mol%, i.e. between 0.15 and 0.50wt%) than traditional metal-based catalysts. The efficiency of guanidine derivatives seems to be related to their nucleophilicity, whereas that of phosphonic acid derivatives depends on their acidity. However, the solubility of the considered species in the reactive medium also plays a major role. The water/alcohol selectivity of the catalysts, especially at room temperature, was then examined as an additional criterion. Guanidines are not selective and favor the reaction of isocyanate groups with water as much as that with alcohols. Phenyl phosphonic acid derivatives are more selective, and particularly pentafluorophenyl phosphonic acid displays a remarkable catalytic activity together with an acceptable selectivity and could represent an interesting and safer alternative to toxic tin and mercury derivatives for many industrial polyurethanes

The auto-oxidation of trans-1,2-disiloxybenzocyclobutene was found to be very efficient, giving endo-peroxide in quantitative yield. Each step of the mechanism of spin-forbidden addition of triplet oxygen O2((3)Σg) was studied by both EPR/spin trapping and theoretical studies.

An efficient and rapid synthesis of the CDEF ring system of lactonamycinone is reported via a highly chemo- and diastereoselective intermolecular Diels-Alder cycloaddition between trans-1,2-disilyloxybenzocyclobutene and the appropriate γ-alkylidenebutenolide. The feasibility and the total chemoselectivity of the [4 + 2] cycloaddition for the construction of a spirolactone moiety via an intramolecular approach (IMDA) using both partners is also described demonstrating the versatility of the γ-alkylidenebutenolide building block.

An efficient synthesis of deoxy-lambertellols was reported through a highly chemo-and diastereoselective intermolecular Diels-Alder cycloaddition between trans-1,2-disiloxybenzocyclobutenes and 2-methylprotoanemonine. Such transformation with d-substituted calkylidenebutenolides, to prepare new analogues of these tricyclic spirolactones, which would be very difficult to prepare by other ways, was also studied.

Preparation of Functionalized Lithium, Magnesium, Aluminum, Zinc, Manganese-, and Indium Organometallics from Functionalized Organic Halides. -[149 refs. + subrefs.]. -(DAGOUSSET, G.; FRANCOIS, C.; LEON, T.; BLANC, R.; SANSIAUME-DAGOUSSET, E.; KNOCHEL*, P.; Synthesis 46 (2014) 23, 3133-3171, http://dx.

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A new, highly efficient and mild N-heterocyclic carbene (NHC)-mediated organocatalytic procedure for the transfer of tin from tributyl(trimethylsilyl)stannane (Bu 3 SnSiMe 3 ) onto aldehydes for the preparation of a-silyloxyalkylstannanes and g-silyloxyallylstannanes has been developed.