Enantioselective monoreduction of 2-alkyl-1,3-diketones mediated by chiral ruthenium catalysts. dynamic kinetic resolution

The reduction of 2-alkyl-1,3-diketones using (R,R)- or (S,S)-RuCl[N-(tosyl)-1,2-diphenylethylenediamine](p-cymene) in the presence of formic acid and triethylamine affords syn-2-alkyl-3-hydroxy ketones as the major products with high enantioselectivity. [reaction: see text]     

Enantioselective approaches to potential MetAP-2 reversible inhibitors

[reaction: see text] Enantioselective deprotonation of 4-substituted cyclohexanones and highly stereoselective conjugate addition of higher order mixed cuprates were the key steps in a concise synthesis of fumagalone-related molecules. The origin of the (low) biological activity of the new compounds as compared to fumagalone is briefly discussed.     

Ring-rearrangement metathesis of substituted dihydropyrans and dihydrofurans

The rearrangement of dihydropyrans and dihydrofurans featuring appending olefins has been studied. The rearranged products bear resemblance with polyunsaturated di- and trisaccharides. Examples of functionalization prior to, or following, rearrangement are provided suggesting that the method should be useful for the synthesis of nonclassical saccharides. This work also illustrates the power of cascade methatetic processes for increasing molecular complexity starting from relatively simple heterocycles.     

Stein’s method for diffusive limits of queueing processes

Queueing Systems - Donsker’s theorem is perhaps the most famous invariance principle result for Markov processes. It states that, when properly normalized, a random walk behaves...     

New synthesis of benzo[b]furan and indole derivatives from 1,1-dibromo-1-alkenes using a tandem Pd-assisted cyclization-coupling reaction

We report a new flexible method for the synthesis of 2-functionalized benzo[b]furans and indoles from readily available o-(2,2-dibromovinyl)-phenol, -aniline or -acetanilide using a tandem Pd-assisted cyclization-coupling reaction.     

Synthesis of the c14-c25 subunit of bafilomycin A1

The enantioselective synthesis of the C14-C25 subunit of bafilomycin A1 was realized in a convergent route. The sequence involves two dynamic kinetic resolution steps of 2-alkyl 1,3-diketones that use optically active ruthenium complexes, an anti-selective reduction of a beta-hydroxyketone to control the C23 stereogenic center, and an aldol-type reaction under Evans' conditions, which sets the C17 and C18 stereogenic centers.     

A new, ring closing metathesis-based synthesis of (-)-fumagillol

[reaction: see text]. A new strategy to access the fumagillin/fumagillol skeleton is proposed. An Evans aldolization and a RCM involving an enone are used for the preparation of a key cyclohexanone intermediate, which was readily converted to fumagillol. The synthesis also features an efficient preparation of isogeraniol and isogeranic acid.     

Mechanical properties of unsaturated polyester resins in relation to their chemical structure. I. Secondary relaxations and local motions

Dynamic mechanical spectroscopy has been combined with high-resolution solid-state ¹³C NMR to characterize the molecular motions responsible for the γ and β secondary relaxations in unsaturated polyester networks. In DEG networks the 7γ transition is assigned to restricted phenyl group rotation in the styrene cross-links whereas the motion of molecular groups in the vicinity of the residual maleic double bonds account for the β transition. © 1994 John Wiley & Sons, Inc.     

Mechanical properties of unsaturated polyester resins in relation to their chemical structure: 2. Plastic deformation behavior

The plastic deformation behavior of unsaturated polyester (UP) networks has been investigated in compression at constant strain-rate over a wide temperature range. The temperature evolution of the activation parameters is directly related to the local molecular dynamics of the different networks previously characterized by dynamic mechanical spectroscopy and high resolution ¹³C solid-state NMR. © 1994 John Wiley & sons, Inc.     

Controlled synthesis of cis or trans isomers of 1,3-disubstituted tetrahydroisoquinolines and 2,5-disubstituted pyrrolidines

[reactions: see text] The stereoselective outcome of Pd(II)- or Ag(I)-catalyzed intramolecular N-alkylation to afford 1,3-disubstituted 1,2,3,4-tetrahydroisoquinolines was examined. In the absence of additional substituents, Pd(II) allows a facile access to the cis isomers, while Ag(I) favors formation of the trans isomers. The same observation was made for the synthesis of 2,5-disubstituted pyrrolidines. Possible reasons for the observed stereoselectivities are discussed.