{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,30]],"date-time":"2026-09-30T05:58:24Z","timestamp":1790747904422,"version":"4.1.0"},"reference-count":27,"publisher":"SAGE Publications","issue":"3","license":[{"start":{"date-parts":[[2026,7,1]],"date-time":"2026-07-01T00:00:00Z","timestamp":1782864000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by-nc\/4.0\/"},{"start":{"date-parts":[[2026,7,1]],"date-time":"2026-07-01T00:00:00Z","timestamp":1782864000000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/journals.sagepub.com\/page\/policies\/text-and-data-mining-license"}],"funder":[{"name":"IOI Investment Zrt."},{"name":"Hungarian National Research Development"},{"name":"Innovation Office University Research Scholarship Programme","award":["EK\u00d6P-25-2-BME-162"],"award-info":[{"award-number":["EK\u00d6P-25-2-BME-162"]}]}],"content-domain":{"domain":["journals.sagepub.com"],"crossmark-restriction":true},"short-container-title":["Science Progress"],"published-print":{"date-parts":[[2026,7]]},"abstract":"<jats:p>\n                    The pyridine-mediated tandem Knoevenagel condensation\u2013decarboxylation of glyoxylic acid and malonic acid was investigated at 95 \u00b0C in neat anhydrous pyridine to establish the mechanistic basis of its strict substrate specificity and to characterise the coordination compound formed during lead(II) acetate-mediated product isolation. Fumaric acid was isolated in 92% yield with confirmed\n                    <jats:italic toggle=\"yes\">trans<\/jats:italic>\n                    -stereoselectivity. Control reactions with glycolic acid, succinic acid, and DL-malic acid as structural analogues of the methylene component uniformly failed to afford fumaric acid, establishing the mechanistic indispensability of three concurrent properties unique to malonic acid: high methylene C\u2013H acidity (p\n                    <jats:italic toggle=\"yes\">K<\/jats:italic>\n                    a = 2.83), resonance-stabilised enolate nucleophilicity, and the \u03b2-keto acid intermediate geometry enabling facile six-membered cyclic decarboxylation. Density functional theory calculations at the r2SCAN-3c\/SMD (pyridine) level show that direct decarboxylation via transition state TS4b is preferred over the competing dehydration\u2013decarboxylation sequence via TS4a by \u0394\u0394G\n                    <jats:sub>solv<\/jats:sub>\n                    <jats:sup>\u2021<\/jats:sup>\n                    = 9.5 kcal mol\n                    <jats:sup>-1<\/jats:sup>\n                    . Treatment of the product with lead(II) acetate yielded an unexpected white precipitate characterised by HR-ESI-MS, titrimetric lead determination, elemental analysis, and PXRD as the coordination polymer [PbO(C\n                    <jats:sub>4<\/jats:sub>\n                    H\n                    <jats:sub>2<\/jats:sub>\n                    O\n                    <jats:sub>4<\/jats:sub>\n                    )]\u00b73H\n                    <jats:sub>2<\/jats:sub>\n                    O, rather than the dihydrate salt [Pb(C\n                    <jats:sub>4<\/jats:sub>\n                    H\n                    <jats:sub>2<\/jats:sub>\n                    O\n                    <jats:sub>4<\/jats:sub>\n                    )]\u00b72H\n                    <jats:sub>2<\/jats:sub>\n                    O reported previously. HR-ESI-MS isotopic pattern analysis confirms a polymeric rather than discrete molecular architecture. This result resolves a century-old structural discrepancy between the Rieckher (1844) and Weiss\u2013Downs (1923) reports, attributing the divergent product architectures to counter-anion-controlled local pH during precipitation. Optimised Cartesian coordinates, total energies, zero-point vibrational energy corrections, and imaginary frequencies for all DFT-located stationary points are provided in the Supplementary Information.\n                  <\/jats:p>","DOI":"10.1177\/00368504261477972","type":"journal-article","created":{"date-parts":[[2026,8,10]],"date-time":"2026-08-10T20:22:57Z","timestamp":1786393377000},"update-policy":"https:\/\/doi.org\/10.1177\/sage-journals-update-policy","source":"Crossref","is-referenced-by-count":0,"title":["Pyridine-mediated tandem Knoevenagel condensation-decarboxylation: Chemoselectivity, mechanistic rationale, and discovery of a novel Lead(II) fumarate coordination polymer"],"prefix":"10.1177","volume":"109","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-9097-6741","authenticated-orcid":false,"given":"Zolt\u00e1n","family":"K\u00f6nt\u00f6s","sequence":"first","affiliation":[{"name":"IOI Investment Zrt"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0000-1647-5471","authenticated-orcid":false,"given":"M\u00e1t\u00e9","family":"Bartek","sequence":"additional","affiliation":[{"name":"Budapest University of Technology and Economics"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"179","published-online":{"date-parts":[[2026,8,10]]},"reference":[{"key":"e_1_3_7_2_2","doi-asserted-by":"publisher","DOI":"10.1002\/cber.19010340111"},{"key":"e_1_3_7_3_2","doi-asserted-by":"crossref","unstructured":"Gao H Luo Z Ge P et al. 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