High pressure and selectivity in organic reactions

Ultra-high selectivity pulsed plasmachemical deposition reaction pathways

Glycidyl methacrylate pulsed plasmas have been investigated using time-resolved in situ mass spectrometry. At low pulsed plasma duty cycles, monomer fragmentation leading to the formation of polymerisation initiator species occurs within each short electrical discharge pulse (t_on = microseconds timescale). This is followed by conventional step-wise monomer addition polymerisation occurring during the subsequent extended off-period (t_off = milliseconds timescale), culminating in the growth of well-defined poly(glycidyl methacrylate) chains. Key attributes associated with this high selectivity pulsed plasmachemical functional thin film synthesis approach are the absence of the requirement for any additional chemicals (catalyst, solvent, etc.) in combination with very low power consumption (mW) and ambient temperature.

Hydrophobicity and mixing effects on select heterogeneous, water-accelerated synthetic reactions

The influence of aqueous reaction media on organic reactions is a topic of long-standing interest, particularly as it affects the rate or selectivity of synthetic reactions. Sometimes such reactions appear homogeneous, typically in dilute solution, whereas others are obviously heterogeneous, typically in concentrated solution that is more characteristic of a preparative synthetic reaction. The latter situation has been termed "on water." Here, it is demonstrated that the rates of heterogeneous ene reactions, Passerini reactions, and Ugi reactions in pure water and in aqueous solutions are dependent on the mixing method and reactant polarity, consistent with the involvement of hydrophobic interactions in their acceleration.

Multicomponent Reactions with Dihydroazines: Efficient Synthesis of a Diverse Set of Pyrido-Fused Tetrahydroquinolines

A multicomponent assembly of pyrido-fused tetrahydroquinolines is accomplished in a one-pot process from the interaction of dihydroazines, aldehydes, and anilines. A rational screening of the different components and parameters of this reaction, such as the range of reactive starting materials, catalysts and reaction conditions (solvent range; thermal, high pressure- and microwave-promoted processes) is carried out. Optimized conditions allow an efficient preparation of pyrido-fused tetrahydroquinolines with good yields, bypassing the biomimetic NADH-like reductive pathway which is typical in the interaction of dihydropyridines with carbonyl compounds and amines. Furthermore, solid-supported versions of the process have been developed, which should facilitate the preparation of libraries.

Diastereoselective Syntheses of New Analogues of the Farnesyltransferase Inhibitor RPR 130401

The access to several benzo[f]perhydroisoindolic analogues of farnesyltransferase inhibitors from a single dienic precursor is reported. An initial [4 + 2] cycloaddition between diphenylisobenzofuran6 and pyrrolines 11, 14, and 15 led to either the syn or the anti isomers, depending on the mode of activation of the cycloaddition. The syn diastereomers were isolated in 90% de under 12 kbar at room temperature, while their anti counterparts were obtained with the same selectivity by warming the reaction mixture to 110 degrees C in toluene at atmospheric pressure. Both syn and anti adducts were separately N-deprotected, and the resulting amines reacted with an activated ester derived from the acid (20) to afford the final targets (5). Two new analogues (5a and 5b) of the FT inhibitor RPR 130401 were thus synthesized in a mere three-step synthetic scheme with overall yields from 30 to 60%.

Thermal/hyperbaric heterocycloaddition of 1,4-dialkoxy-1,3-dienes: the de novo (E,Z) way to sugars

1-(Z)-Alkoxy-4-(E)-methoxybutadiene derivatives have been reacted with ethylgyoxylate and diethyl ketomalonate under thermal or hyperbaric conditions. They provide, with a total regioselectivity and fair to total endoselectivities, the expected dihydropyranic cycloadducts. Three of those pseudo-glycals have been converted in a few classical steps (deprotection, reduction, and dihydroxylation) into (racemic) allose, mannose, and gullose derivatives. The order of these three steps has a direct influence on the efficiency of the transformation and determines the stereochemistry of the final sugar.

The use of high pressure for separation and production of bioactive molecules

Due to its action on the forces governing inter- and intramolecular interactions, the application of high pressure to biopurification or bio-elaboration of a product are of interest. The two closely thermodynamically related parameters, pressure and temperature, render processes based on their action clean, as no chemical reagents have to be added (and thus further removed) when they are applied. The use of high pressure in the development of desorption methods for the purification of bioactive molecules, particularly in the immunoaffinity field, is reviewed and discussed. Also mentioned is the application of the pressure parameter during the synthesis of a bioreagent. Finally, integrated processes relative to the synthesis and purification of these compounds are proposed.

Sonochemistry of carbohydrate compounds

A literature survey of carbohydrate sonochemistry is presented. The basic physical principles are discussed qualitatively before the main applications are reviewed. Along with other non-classical activation methods developed in accordance with 'Green Chemistry' requirements, ultrasonic irradiation offers important potential for the conversion of biomass raw materials such as polymeric carbohydrates to useful lower weight molecules. A number of reactions involving mono- or disaccharides, considered as a renewable source of fine chemicals, can also be performed with ultrasonic activation. This is the case for glycosylation, acetalization, oxidation, C-D, C-heteroatom, and C-C bond formations, which are improved in terms of reaction rates and yields and, in some instances, in their chemo-, regio- and stereoselectivities. The equipment available is briefly described, and practical considerations are given.