- Transition Metal-Free Trans Hydroboration of Alkynoic Acid Derivatives: Experimental and Theoretical Studies
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We report a phosphine-catalyzed trans hydroboration of alkynoate esters and amides. The reaction proceeds under mild conditions with exclusive (E)-selectivity to afford (E)-β-boryl acrylates and (E)-β-boryl acrylamides in good to excellent yields. The reaction is tolerant of a variety of functional groups and allows efficient access to novel oxaboroles as well as a pargyline derivative (MAO inhibitor). Theoretical calculations suggest an internal hydride generates a phosphonium allenoxyborane followed by the formation of a key phosphonocyclobutene intermediate that collapses in a stereoselective, rate-limiting step.
- Fritzemeier, Russell,Gates, Ashley,Guo, Xueying,Lin, Zhenyang,Santos, Webster L.
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p. 10436 - 10444
(2018/07/21)
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- One-pot synthesis of trisubstituted monomethylated benzene-1,3-diols via a Michael addition-Dieckmann cyclization sequence from methyl (E)3-methoxy-4- methoxycarbonylbut-2-enoate anion and methyl alkynoates and its application to the total synthesis of nidulol
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The reaction of methyl (E)3-methoxy-4-methoxycarbonylbut-2-enoate (1) with a number of methyl alkynoates under appropriate conditions gave the monomethylated trisubstituted resorcinol derivatives 3 in a regiocontrolled manner, via a Michael addition-Dieckmann cyclization sequence in one pot. The resorcinol 3d, prepared in this manner, was used as the starting material for a three step, highly efficient (54% from 3d) synthesis of the bioactive fungal metabolite nidulol (4). Georg Thieme Verlag Stuttgart.
- Covarrubias-Zuniga, Adrian,San German-Sanchez, Laura,Maldonado, Luis A.,Romero-Ortega, Moises,Avila-Zarraga, Jose G.
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p. 2293 - 2296
(2007/10/03)
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- Regio- and diastereoselective allenylation of aldehydes in aqueous media: Total synthesis of (+)-goniofufurone
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The regio- and diastereoselectivities of metal-mediated allenylation of carbonyl compounds were investigated in aqueous media. Different metal mediators showed varied regioselectivities on product formation during propargylation-allenylation reactions of carbonyl compounds with simple propargyl bromide. Under the standard reaction conditions, the use of indium provided the highest regioselectivity, with a preference of formation of the homopropargyl alcohol. The use of tin and bismuth as the metal mediator provided slightly lower selectivities with the same preference. The use of zinc and cadmium as the mediators further lowered the product selectivity. The reactions of an alipathic aldehyde with simple propargyl bromide showed a lower selectivity than the reaction of an aromatic aldehyde in most cases, except for the use of tin or zinc (where comparable selectivities were observed). On the other hand, the reaction of terminal-substituted propargyl bromides with aldehydes mediated by indium showed a high regioselectivity in forming allenylation products. The indium-mediated allenylation of carbonyl compounds bearing an α-hydroxyl group also proceeded with a high diastereoselectivity, forming syn-diols predominantly in aqueous ethanol. The high diastereoselectivity in allenylation of α-hydroxyl-substituted aldehydes was attributed to the chelation effect exhibited by the α-hydroxyl substituent. Through the use of this highly diastereoselective allenylation, (+)-goniofufurone was synthesized from D'-glucurono-6,3-lactone.
- Yi, Xiang-Hui,Meng, Yue,Hua, Xiao-Gang,Li, Chao-Jun
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p. 7472 - 7480
(2007/10/03)
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