| Reference | [1]. Cross-Coupling Reactions Enabled by Dual Gold/Palladium Catalysis<br />
Patil, N. T.; Tathe, A. G.; Bhoyare, V. W., Science of Synthesis: Dual Catalysis in Organic Synthesis, (2019) 1, 127.<br />
After gathering tangible mechanistic proof for gold/palladium transmetalation and the successful development of cross-coupling reactions featuring various organogold(I) reagents under palladium catalysis, the advanced version, i.e. cross-coupling reactions involving dual gold/palladium catalysis, was sought. Nevertheless, this process has its own set of challenges. First, getting the simultaneous turnover of the two metals is arduous. Secondly, the stability of palladium or gold intermediates generated in situ toward protodemetalation or reaction with other species present is always a matter of concern. Lastly, the key transmetalation step between the two catalytic species, present in scarce amount in the reaction media, also requires exquisite control.<br />
DOI: 10.1055/sos-SD-231-00061<br />
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[2]. Palladium-Mediated Cascade Cross-Coupling/Electrocyclization Approach to the Construction of Fused Bi- and Tricyclic Rings<br />
Ipaktschi, J.; Saidi, M. R., Science of Synthesis Knowledge Updates, (2011) 3, 495.<br />
A palladium(0) catalyst initiates the cascade polycyclization reactions of bromo-1,6-enyne ‌425‌ with tributyl(prop-1-enyl)- and tributyl(penta-1,3-dienyl)stannanes. Overall, the process achieves the formation of three carbon–carbon bonds and two rings in a single step<br />
DOI: 10.1055/sos-SD-140-00042<br />
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[3]. Variation 5: Lewis Acid Catalyzed Addition of Alkenylmetals to Carboxylic Acid Halides and Anhydrides<br />
Marsden, S. P., Science of Synthesis, (2005) 26, 1055.<br />
Alkenylsilanes undergo regio- and stereospecific Friedel–Crafts intermolecular acylation reactions with acid halides under activation by strong Lewis acids.[‌47‌,‌48‌] The reaction of (E)-alkenylsilane ‌48‌ occurs with ipso substitution of the silicon and retention of alkene geometry to yield (E)-enone ‌49‌ (‌Scheme 12‌), both effects being governed by the formation of a silicon-stabilized β-cation. By contrast, the reactions of vinylstannanes with acid chlo­rides and anhydrides yield trans-enones regardless of the configuration of the starting vinylstannane, as illustrated by the convergence of a mixture of geometric stannane isomers ‌50‌ to a single isomeric enone ‌19‌.[‌49‌] The intramolecular reaction of acid halides with vinylsilanes generally proceeds as for the intermolecular reactions (e.g., in the conversion of ‌51‌ into ‌52‌)[‌50‌] but anomalous regio- and stereochemical outcomes are occasionally observed in this manifold. Thus, acid chloride ‌53‌ is converted into 3-methylcyclohex-2-en-1-one (‌2‌) by attack at the β-carbon to the silicon, followed by a Wagner–Meerwein shift of a methyl group, loss of silicon, and alkene isomerization.<br />
DOI: 10.1055/sos-SD-026-00987<br />
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[4]. Method 1: Intramolecular Elimination<br />
Sato, S.; Furukawa, N., Science of Synthesis, (2005) 18, 855.<br />
There are several examples of the preparation of acyclic and cyclic thiocarbonate O,O-esters, which are used as synthetic intermediates. For example, optically active methyl cyclopropanoate ‌124‌ is converted, with retention of stereochemistry, on treatment with O-4-tolyl chlorothioformate and pyridine into the thiocarbonate O,O-ester ‌125‌ in 80% yield. The thiocarbonate O,O-ester ‌125‌ undergoes Chugaev-type elimination to give optically pure cis-chrysanthemic acid methyl ester (‌126‌) in 90% yield (‌Scheme 54‌).<br />
DOI: 10.1055/sos-SD-018-00970<br />
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[5].Method 2: Stille Coupling<br />
Spitzner, D., Science of Synthesis, (2005) 15, 244.<br />
Stille coupling of stannanes with halopyridinium salts, e.g. ‌1045‌, in the presence of palladium(0) and copper(I) iodide as cocatalyst gives the coupling products ‌1046‌ in moderate yields (‌Scheme 352‌). The yields increase when tris(dibenzylideneacetone)dipalladium(0), together with tri(2-tolyl)phosphine, is used as a catalyst.<br />
DOI: 10.1055/sos-SD-015-00002
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