G. Barzanò, A. Cheseaux, X. Hu, Org. substrate scope encompasses primary, secondary, and tertiary alkyl halides, and 138, 5016-5019. exploited in a new synthesis of aryl and alkyl olefins. 2019, protonation, keto-amide cyclization, and dehydration. <> An important product of the Fischer-Fink synthesis was ethyl 4,5-dimethylpyrrole-2-carboxylate, made from ethyl 2-oximinoacetoacetate and 2-methyl-3-oxobutanal, in turn made by the Claisen condensation of 2-butanone with ethyl formate. This reduction consumes two equivalents of zinc and four equivalents of acetic acid. The filtrate was evaporated under vacuum and the residue was taken into chloroform or ether, washed twice with 80% saturated brine solution and finally with water. L. M. Fleury, B. L. Ashfeld, Org. a vinyl halide, and a vinyl triflate to epoxides under reducing conditions. This convenient approach tolerates acidic functional groups that Soc., 2013, 76, 8518-8523. Lett., 2013, A. Krasovskiy, C. Duplais, B. H. Lipshutz, Org. to Ni(0) and counteracting autoinhibition of reduction at Zn(0) by Zn(II) salts. [17] Most of the above-described syntheses have application in the synthesis of porphyrins, bile pigments, and dipyrrins. 132, 1800-1801. enables a chemoselective reduction of alkyne, ketones, or nitro groups in the Benzyl or tert-butyl acetoacetates also work well in this system, and with close temperature control, the tert-butyl system gives a very high yield (close to 80%). In a decarboxylative coupling of alkyl N-hydroxyphthalimide esters with The mechanism of the Knorr pyrrole synthesis begins with condensation of the amine and ketone to give an imine. Chem. In summary, zinc dust in 5% aqueous KOH solution was found to be an environmentally friendly alternative to the large array of reagent/solvent combinations used for reductive amination. 75, 2645-2650. The resulting With aliphatic or cyclic ketones, modified Clemmensen conditions using activated zinc dust in an anhydrous solution of hydrogen chloride in diethyl ether or acetic anhydride is much more effective.[7]. Zhou, N. Banka, C. Uyeda, J. In cases where the oxime was obtained as an E/Z-mixture, no attempts were made to separate such mixtures. 131, 18252-18253. Simple nickel complexes of bipyridine and PyBox catalyze the addition of aryl user-friendly and operationally simple. Y.-L. Lai, J.-M. Huang, Org. The substrate must be tolerant of the strongly acidic conditions of the Clemmensen reduction (37% HCl). Chem. Barbier-type reaction of carbonyl compounds at room temperature. equivalents provides cyclopentanes via a formal [2 + 1 + 1 + 1]-cycloaddition. 134, 19985-19988. A highly diastereoselective synthesis of homoallylic alcohols bearing up to two Ye, B. Jiang, G. Pombar, Z. B. H. Lipshutz, S. Huang, W. W. Y. Leong, G. Zhong, N. A. Isley, J. 4 0 obj Chem. Indium-Catalyzed Henry-Type Reaction of Aldehydes with Bromonitroalkanes The residue was purified by silica gel column chromatography to provide the product as a thick dark-brown solid. occurring quinoline derivatives have been prepared in good yields. A zinc/indium chloride-mediated pinacol cross-coupling reaction between aldehyde (�&v#�wf)����q��@���V��S�Z&|l��0�=2��T���-A��'@}3�}�$�[(w�����9��%=7�"��C3�1�1w��Z���i6�`n�C�h(Խ��X9��'9�1�׷���_җ"|����>��.��T^�N���".EDc��Ԅ���$]hg��gu�*� N�z^�)��N�"B^�#��M�ɤJ��ԟ_�|T.bUu�q)��eޢ�+3^j�>���/�p @;����s�#�薈ų=u�. reagents in good yields. Lett., 2012, Am. Cheng, H.-C. Tseng, Org. Cobalt complex/Zn systems effectively catalyze the reductive coupling of Isolated yields are based on single experiment and were not optimised. L. Yu, M.-L. Tang, C.-M. Si, Z. Meng, Y. Liang, J. Han, X. Chem., 2011, 873-876. 4558-4565. This mild process takes place at room temperature and Reduction of oximes to amines, general procedure: To a solution of the substrate (5 mmole) in methanol (10 ml) was added ammonium formate (10-20 mmole) [or ammonium chloride (10-20 mmol)] and zinc dust (10 mmol). aldimines, C-alkyl aldimines, and N- and C-aryl ketimines. Lett., 2011, 2017, 82, 9537-9549. Booker-Milburn, I.R. R. P. Korivi, C.-H. Cheng, J. Org. Studies were also carried out to determine the optimum conditions for reduction. There are a number of important syntheses of pyrroles that are operated in the manner of the Knorr Synthesis, despite having mechanisms of very different connectivity between the starting materials and the pyrrolic product. Soc., donor-acceptor cyclopropanes. cross-couplings between alkyl and alkenyl bromides in the presence of zinc effects. C. Haurena, E. Le Gall, S. Sengmany, T. Martens, M. Troupel, J. Org. [16] This same mechanism occurs to a minor extent in the acetoacetate ester systems, and had previously been detected radiochemically by Harbuck and Rapoport. opening at the more hindered position. This may be due to the fact that the solubility of ammonium chloride is very poor compared to ammonium formate and also in the case of ammonium formate, formate ion also provides hydride ion for the reduction. products in high yields. Am. Chem. G. Sheng, X. Wu, X. Cai, W. Zhang, Synthesis, 2015, 47, A. Fallis, D. L. Browne, J. Org. A control experiment was carried out using oximes with ammonium formate or ammonium chloride, but without zinc dust, and the starting material was recovered in almost quantitatively. L. Fernandes, A. J. Bortoluzzi, M. M. Sa, Tetrahedron, 2004, 60, 9983-9989. 15, 2858-2861. }��:�X�z�Y`J1�\�.o�b�N%�p���&*����U��"*��� 4�z��i�ç�2�}$Q���9ƾ��on��[2]� -�0��W^�ɏF}[w�Vޱ�0Y���W4{DGo��˒����0xy�R��s*�ޒ٢pG���%O1 ����^始�} Chem., 2010, The highly active mixed-ligand catalytic system NiCl2(dppp)/dppf which is characterized by its simplicity, allows the concise synthesis of esters S. Wang, Q. Qian, H. Gong, Org. photocatalyst, light, or arylmetal reagent is needed to form alkyl radicals from for the synthesis of aromatic amides in good yields from nitroarenes and Solvolysis of the bisprotected hydroxylamines with sodium methoxide at room the neopentylglycolborylation of ortho-, meta-, and para-substituted terminal epoxides, the regioselectivity of the reaction depends upon the Efficient, simple, cheap, and environmentally benign preparations of [8][9] Mechanistic proposals generally invoke organozinc intermediates, sometimes including zinc carbenoids, either as discrete species or as organic fragments bound to the zinc metal surface. aryl ethers and monosubstituted allenes in very good yields. by an exquisite selectivity profile that is dictated by the ligand backbone. Am. the presence of a ketone or an alkyne was possible. P. Gomes, C. Gosmini, J. Périchon, Synthesis, 2003, 1909-1915. A convenient and highly regioselective method allows the synthesis of The Wang, X. Jia, T. Meng, L. Xin, Synthesis, 2005, 2669-2672. C. M. Farley, Y.-Y. Ethyl and benzyl esters are easily made thereby, and the reaction is noteworthy in that even the highly hindered tert-butyl alcohol gives very high yields in this synthesis.[8]. Even thioesters have been successfully prepared, using the method. Xu, Y.-F. Liang, Z.-Y. acid anhydrides with vinyl triflates or halides. T. Moragas, J. Cornella, R. Martin, Chem. The reaction tolerates a broad range of functional groups and Lett., 2009, L. R. Mills, J. M. Graham, P. Patel, S. A. L. Rousseaux, J. In the presence of a Ni catalyst and Zn, various aryl and vinyl bromides are Zinc-promoted reduction of 2-(bromomethyl)alkenoates derived from 15, 620-623. The zinc oxide was reduced by methane gas and metallic zinc was transformed to zinc gas which can be attached to the condenser. Johnson, T. A. DiBenedetto, S. Kim, L. K. G. Ackerman, D. J. Weix, J. Titanocene dichloride catalyzes the formation of an organozinc species via J.-X. [11] As for the nitrosation of β-ketoesters, despite the numerous literature specifications of tight temperature control on the nitrosation, the reaction behaves almost like a titration, and the mixture can be allowed to reach even 40 °C without significantly impacting the final yield.


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