The stabilisation of 3,4-pyridyne (1) by an alkoxy group adjacent to the ring nitrogen is reported. The regioselective lithiation of 2-ethoxy- (14), 2-methoxy- (18), 2-isopropoxy- (19) and 6-isopropoxy- (26) -3-chloropyridines with tert-butyllithium at low temperatures, followed by elimination of lithium chloride affords 2- and 6-alkoxy-3,4-pyridynes. These species are trapped in situ with furan in a Diels–Alder reaction to give 5–8 in 66–89% yield, and do not give products typical of polymerisation or nucleophilic addition to the 3,4-pyridyne intermediates. As a comparison treatment of 3-chloropyridine with furan and LDA gives only 19% of adduct (4). We also report the novel use of the isopropoxy (rather than methoxy) group in these systems, which can act as a heteroatomic electron donating group which inhibits α-lithiation by tert-butyllithium because of its increased steric bulk.
Crossed products: Ortho-substituted benzaldehydes react with other aromatic aldehydes in a highly selective, atom-economical Tishchenko disproportionation (see scheme) in the presence of a readily prepared, inexpensive thiolate-based catalyst. The methodology is of exceptionally wide scope and exhibits a high functional-group tolerance.
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Desymmetrizations of meso anhydrides catalyzed by a cinchona alkaloid bearing a thiourea moiety are reported. Bifunctional catalyst 1 mediates the methanolysis of succinic and glutaric anhydrides 2 to give hemiesters 3 in good yields and enantioselectivities. The reactions are carried out in coordinating solvents at unusually low concentrations to prevent the dimerization or aggregation of catalyst 1 through hydrogen bonding. Its monomeric form is presumably responsible for high enantioselectivities.
The first study of the cycloaddition of benzaldehyde with homophthalic anhydride under the influence of an alkaloid-based, squaramide substituted bifunctional organocatalyst using DFT methodology is reported.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Imidazolium Brønsted acidic catalysts substituted with ester/amides have been assessed for both antimicrobial toxicity and biodegradation. Low toxicity to a screen of 20 microbial strains (12 fungi and 8 bacteria) was demonstrated. Imidazolium salts incorporating either ester or amide groups at N-1, C-2, C-4 and C-5 did not pass the readily biodegradable test (ISO 14593). Catalyst selection based on Traffic Signal Light classification of performance, (eco)toxicity, and efficient synthesis is described.
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