Coupling-isomerization synthesis of chalcones

The Sonogashira coupling of electron-deficient (hetero)aryl halides 1 and (hetero)aryl or alkenyl 1-propargyl alcohols 2 does not terminate at the stage of the expected internal propargyl alcohols, but rather gives rise to the formation of alpha,beta-unsaturated ketones 3 with a variety of acceptor substituents. This new domino reaction, a coupling-isomerization reaction (CIR), can be rationalized as a sequence of rapid Pd/Cu-catalyzed alkynylation followed by a slow amine-base-catalyzed propargyl alcohol-enone isomerization. Performing the CIR in deuterated protic solvents or with a selectively deuterated propargyl alcohol revealed that the base-catalyzed isomerization step proceeds through a formal 1,3-H shift with minimal H/D exchange with the surrounding solvent. Additionally, 19F NMR kinetic measurements on the isomerization step with the fluorinated propargyl alcohol 4 r support the mechanistic rationale.     

The synthesis and properties of zeolite CF-3

The novel zeolite CF-3, with a high ratio of SiO₂/Al₂O₃ and a characteristic X-ray powder diffraction pattern, has been synthesized hydrothermally from a TMEDA-Na₂O–SiO₂–Al₂O₃–H₂O system at 200°C. The molar composition of CF-3 is (0.4–0.6)Na₂O·(1.5–6.3)TMEDA·Al₂O₃·(80–400)SiO₂·(0–17)H₂O·CF-3 is similar to ZSM-39 and melanophlogite, which have a clathrate-type structure.     

Dimethylzinc-mediated, enantioselective synthesis of propargylic amines

A one-pot, enantioselective synthesis of N-aryl propargylic amines, using alkynylation reagents obtained from dimethylzinc and terminal acetylenes in combination with various aldehydes and o-methoxyaniline as starting materials, has been developed. Enantiopure beta-amino alcohols derived from norephedrine were used as non-covalent chiral auxiliaries, both in stoichiometric or substoichiometric amount. After optimization, propargylic amines were obtained in good to high yields (up to 93%) and with moderate to high enantiomeric excesses (up to 97% ee). The possibility to recover the chiral auxiliary after the reaction was demonstrated.     

Chromatography-free synthesis of Corey's intermediate for Tamiflu

Column chromatography-free stereoselective synthesis of Corey's intermediate for Tamiflu (oseltamivir phosphate) was achieved, starting from l-glutamic acid γ-ethyl ester. The reagents and solvents used in the reaction scheme are industrially tractable, rendering the synthesis a potential starting point for process research.     

Regioselective hydrosilations. II. The synthesis of silicon–hydrogen functional compounds

The discovery that the rhodium-catalyzed hydrosilation of unsaturated epoxides with compounds containing two Si? H functional groups proceeds in a discrete, stepwise fashion, has made possible the synthesis of a series of interesting compounds containing both Si? H and epoxy groups in the same molecule. These compounds can be used both as an interesting new class of epoxy monomers as well as intermediates for the preparation of a wide variety of novel monomers which incorporate epoxide as well as other types of polymerizable functional groups © 1993 John Wiley & Sons, Inc.     

Palladium-catalyzed cross-coupling reactions in total synthesis

In studying the evolution of organic chemistry and grasping its essence, one comes quickly to the conclusion that no other type of reaction plays as large a role in shaping this domain of science than carbon-carbon bond-forming reactions. The Grignard, Diels-Alder, and Wittig reactions are but three prominent examples of such processes, and are among those which have undeniably exercised decisive roles in the last century in the emergence of chemical synthesis as we know it today. In the last quarter of the 20th century, a new family of carbon-carbon bond-forming reactions based on transition-metal catalysts evolved as powerful tools in synthesis. Among them, the palladium-catalyzed cross-coupling reactions are the most prominent. In this Review, highlights of a number of selected syntheses are discussed. The examples chosen demonstrate the enormous power of these processes in the art of total synthesis and underscore their future potential in chemical synthesis.     

Mesogenic quinazolone derivatives: synthesis and characterisation

Two new mesogenic homologous series of quinazolone derivatives have been synthesised by condensation of 4-n-alkoxybenzoyloxy benzaldehyde (for series I) / 4-n-alkoxy-3-methoxybenzoyloxy benzaldehyde (for series II) with 3-amino-2-methyl quinazolone in alcohol. The synthesised compounds are characterised by a combination of elemental analysis and standard spectroscopic methods. In series I, all the synthesised members exhibit the nematic mesophase. An enantiotropic smectic A phase is observed from the n-decyloxy derivative onward to the last homologue synthesised. Methoxy to n-propyloxy derivatives of series II are non-mesogenic, whereas the rest of the members exhibit a monotropic nematic mesophase. The mesomorphic properties of the present series I and II are compared with each other and with the other structurally related mesogenic homologous series to evaluate the effect of lateral methoxy substituent and quinazolone moiety on mesomorphism.