SG1 based alkoxyamines as radical initiators for the synthesis of lactones and lactames

Recently, it has been shown that alkoxyamines can be used as radical initiators in tin-free radical chemistry. Thus, it prompted us to develop the preparation of highly valuable alkoxyamines via ionic chemistry and the radical cyclization was triggered by thermal initiation. Following that procedure, bicyclic, spiro and eight-membered lactones were easily prepared in good yields with very high stereoselectivity.     

Méthode d'homogénéisation auto-cohérente en calcul à la ruptureSelf-consistent homogeneization method in yield design

This work is aimed towards determining the macroscopic strength criterion of a heterogeneous material with a random microstructure. We use the self-consistent concept by considering a reference material, which is of same nature as the constituents of the heterogeneous material. We deduce that the estimates of the macroscopic strength domain are the solutions to self-consistent equations and we give their derivation procedure. To cite this article: S. Turgeman, B. Guessab, C. R. Mecanique 330 (2002) 623–626.     

Computational Studies on Intramolecular Cycloadditions of Azidoenynes and Azidobutenenitriles to Give 6H‐Pyrrolo[1,2‐c][1,2,3]triazoles and 5H‐Pyrrolo[1,2‐d]tetrazoles

Energetics of intramolecular cycloadditions of azidoenynes and azidobutenenitriles to give 6H‐pyrrolo[1,2‐c][1,2,3]triazoles and 5H‐pyrrolo[1,2‐d]tetrazoles have been calculated at the B3LYP/6.311++G(3df,3pd) level of theory in ideal gas and in H₂O as solvent. Stabilities of the corresponding anions, tautomers, and isomers are discussed. Transition states of the cyclization of parent compounds are determined at the same level of theory.     

Competitive Gold‐Promoted Meyer–Schuster and oxy‐Cope Rearrangements of 3‐Acyloxy‐1,5‐enynes: Selective Catalysis for the Synthesis of (+)‐(S)‐γ‐Ionone and (−)‐(2S,6 R)‐cis‐γ‐Irone

We report a simple, highly stereoselective synthesis of (+)‐(S)‐γ‐ionone and (‐)‐(2S,6R)‐cis‐γ‐irone, two characteristic and precious odorants; the latter compound is a constituent of the essential oil obtained from iris rhizomes. Of general interest in this approach are the photoisomerization of an endo trisubstituted cyclohexene double bond to an exo vinyl group and the installation of the enone side chain through a [(NHC)Au^I]‐catalyzed Meyer–Schuster‐like rearrangement. This required a careful investigation of the mechanism of the gold‐catalyzed reaction and a judicious selection of reaction conditions. In fact, it was found that the Meyer–Schuster reaction may compete with the oxy‐Cope rearrangement. Gold‐based catalytic systems can promote either reaction selectively. In the present system, the mononuclear gold complex [Au(IPr)Cl], in combination with the silver salt AgSbF₆ in 100:1 butan‐2‐one/H₂O, proved to efficiently promote the Meyer–Schuster rearrangement of propargylic benzoates, whereas the digold catalyst [{Au(IPr)}₂(μ‐OH)][BF₄] in anhydrous dichloromethane selectively promoted the oxy‐Cope rearrangement of propargylic alcohols.     

Formation of the Main Cores Present in Natural Products by Tandem Additions

A rapid route to 5,5‐ and 5,6‐ bicyclic systems is provided by an 1,3‐alkyl‐shift process mediated by a hypervalent iodine reagent on aromatics. The structures obtained contain several unsaturations with different behaviors and reactivities. Such diversity allows further elaborations for the rapid formation of compact systems present in a variety of natural products. The potential for further transformations has been demonstrated by performing a double Michael addition. This cyclization process is regio‐ and stereoselective due to the presence of a former benzylic substituent. Furthermore, an extension of this approach has been accomplished on indole derivatives.     

A Bistable Microelectromechanical System Actuated by Spin-Crossover Molecules

We report on a bistable MEMS device actuated by spin-crossover molecules. The device consists of a freestanding silicon microcantilever with an integrated piezoresistive detection system, which was coated with a 140 nm thick film of the [Fe(HB(tz)₃)₂] (tz=1,2,4-triazol-1-yl) molecular spin-crossover complex. Switching from the low-spin to the high-spin state of the ferrous ions at 338 K led to a reversible upward bending of the cantilever in agreement with the change in the lattice parameters of the complex. The strong mechanical coupling was also evidenced by the decrease of approximately 66 Hz in the resonance frequency in the high-spin state as well as by the drop in the quality factor around the spin transition.     

Biomimetic synthetic studies on lactonamycin: an expedient synthesis of dihydroxy-isoindolinone-carboxylates

The synthesis of dihydroxy-isoindolinone-carboxylates from a dioxinone keto-ester and N-protected sarcosine without the use of phenolic protection is described. Base-induced aromatization of the dioxinone diketo-ester followed by lactamization furnished the desired dihydroxy-isoindolinone moiety, which could be used as an EF-ring precursor toward the synthesis of lactonamycin.     

Synthesis and application of isocyanates radiolabeled with carbon-11

Carbon-11 labeled isocyanates are efficiently prepared by dehydration of [(11) C]carbamate salts, which in turn are easily formed from cyclotron-produced [(11) C]CO(2) and amines in the presence of a CO(2) fixation agent. The [(11) C]isocyanates are useful radiosynthons for the synthesis of a variety of [carbonyl-(11) C]-labeled asymmetrical ureas and carbamate esters. The method is well suited to incorporate any isotope of carbon, and is especially useful for positron emission tomography (PET) radiotracers for in vivo imaging. This is demonstrated by using the method to make [carbonyl-(11) C]-6-hydroxy-[1,1'-biphenyl]-3-yl cyclohexylcarbamate which is a novel radiotracer for PET imaging of fatty acid amide hydrolase.     

Tagging saccharides for signal enhancement in mass spectrometric analysis

MALDI-MS provides a rapid and sensitive analysis of large biomolecules such as proteins and nucleic acids. However, oligo- and polysaccharides are less sensitive in MS analysis partly due to their neutral and hydrophilic nature to cause low ionization efficiency. In this study, four types of oligosaccharides including aldoses, aminoaldoses, alduronic acids and α-keto acids were modified by appropriate tags at the reducing termini to improve their ionization efficiency. Bradykinin (BK), a vasoactive nonapeptide (RPPGFSPFR), containing two arginine and two phenylalanine residues turned out to be an excellent MS signal enhancer for maltoheptaose, GlcNAc oligomers and oligogalacturonic acids. In the MALDI-TOF-MS analysis using 2,5-dihydroxybenzoic acid (2,5-DHB) as the matrix, the GalA4-BK and GalA5-BK conjugates prepared by reductive amination showed the detection limit at 0.1 fmol, i.e. ～800-fold enhancement over the unmodified pentagalacturonic acids. The remarkable MS enhancement was attributable to the synergistic effect of the basic arginine residues for high proton affinity and the hydrophobic property phenylalanine residues for facile ionization. A tetrapeptide GFGR(OMe) and an arginine linked phenylenediamine (H(2) N)(2) Ph-R(OMe) were thus designed to act as potent tags of oligosaccharides in MS analysis. Interestingly, concurrent condensation and lactonization of α2,8-linked tetrasialic acid (SA4) was carried out with (H(2) N)(2) Ph-R(OMe) to obtain a quinoxalinone derivative, which showed > 200-fold enhancement over unmodified SA4 in the MALDI-TOF-MS analysis.