Evaluation of possible intramolecular [4+2] cycloaddition routes for assembling the central tetracyclic core of the potent marine antiinflammatory agent mangicol A
摘要:
A plan for enantioselective construction of the mangicol A framework by means of intramolecular Diels-Alder cycloaddition is outlined. First to be assembled is the enantiopure cyclopentenecarboxylic acid 16. Of the several approaches targeting the 1,3-diene component 56, only that involving palladium-catalyzed enyne cyclization proved successful. Following the coupling of 16 to 56, we were unable to bring about any detectable level of (4 pi+2 pi) cycloaddition. Activation of the diene by incorporation of an OSiEt3 substituent on a terminal sp(2)-hybridized center likewise proved unsuccessful. Further facilitation was sought in the form of cyclopentenonecarboxylate 66. However, thermal activation, Lewis acid catalysis, and high-pressure conditions proved ineffective and did not lead to C-C bond formation. These studies serve to underscore the extent to which steric complications can complicate matters and the extent to which they must be skirted to arrive at the title compound. (c) 2006 Elsevier Ltd. All rights reserved.
Polystyrene-supported GaCl3: A new, highly efficient and recyclable heterogeneous Lewis acid catalyst for tetrahydropyranylation of alcohols and phenols
作者:Ali Rahmatpour
DOI:10.1016/j.poly.2012.06.063
日期:2012.8
highly chemoselective method for tetrahydropyranylation of alcohols and phenols with 3,4-dihydro-2H-pyran (DHP) in the presence of polystyrene-supported gallium trichloride (PS/GaCl3) as a highly active and reusable heterogeneous Lewisacidcatalyst at room temperature is presented. In this catalytic system, primary, secondary and tertiary alcohols, as well as phenols, were converted to the corresponding
Acetonyltriphenylphosphonium Bromide (ATPB): A Versatile Reagent for the Acylation of Alcohols, Phenols, Thiols and Amines and for 1,1-Diacylation of Aldehydes under Solvent-Free Conditions
作者:Abu T. Khan、Lokman H. Choudhury、Subrata Ghosh
DOI:10.1002/ejoc.200500066
日期:2005.7
A wide variety of alcohols, phenols, amines and thiols may easily be converted into the corresponding acetate derivatives by treatment with acetic anhydride (1.5–2.0 equivalents) in the presence of acetonyltriphenylphosphonium bromide (ATPB; 5 mol %) in good yields at room temperature. With the same precatalyst, both aliphatic and aromatic aldehydes can also be transformed into the corresponding gem-diacetates
The synthesis of hydroxyesters from carboxylic acids and unprotected amino alcohols in both continuous flow and batch processes is reported. The formation of a transient diazonium species with a dinitrite reagent is key in this transformation. The reaction conditions are compatible with a variety of functional groups.
Polystyrene-Gallium Trichloride Complex: A Mild, Highly Efficient, and Recyclable Polymeric Lewis Acid Catalyst for Chemoselective Silylation of Alcohols and Phenols with Hexamethyldisilazane
作者:Ali Rahmatpour、Ali Vakili、Setare Azizian
DOI:10.1002/hc.21109
日期:2013.11
(HMDS) for the efficientsilylation of alcohols and phenols at room temperature. In this heterogeneous catalytic system, primary, secondary, and tertiaryalcohols as well as phenols were converted to their corresponding trimethylsilyl ethers with short reaction times and high yields under mild reaction conditions. The heterogenized catalyst is of high reusability and stability in the silylation reactions
Elaboration of the ether cleaving ability and selectivity of the classical Pearlman's catalyst [Pd(OH)2/C]: concise synthesis of a precursor for a myo-inositol pyrophosphate
作者:Alson Mart、Mysore S. Shashidhar
DOI:10.1016/j.tet.2012.09.016
日期:2012.11
The cleavage of propargyl, allyl, benzyl, and PMB ethers by Pd(OH)2/C can be tuned in that order, by varying the reaction conditions. Other moieties such as C–C double bonds, esters, trityl ether, p-bromo and p-nitrobenzyl ethers are stable to these reaction conditions. Cleavage of allyl ethers can be made catalytic by using 1:1 mixture of Pd(OH)2/C and Pd/C. The synthetic potential of the selective