{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,1]],"date-time":"2026-07-01T06:57:40Z","timestamp":1782889060145,"version":"3.54.5"},"reference-count":57,"publisher":"MDPI AG","issue":"8","license":[{"start":{"date-parts":[[2018,7,31]],"date-time":"2018-07-31T00:00:00Z","timestamp":1532995200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100003329","name":"Ministry of Economy and Competitiveness","doi-asserted-by":"publisher","award":["CTQ2016-78669-P"],"award-info":[{"award-number":["CTQ2016-78669-P"]}],"id":[{"id":"10.13039\/501100003329","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100010751","name":"Fondecyt","doi-asserted-by":"publisher","award":["1180348"],"award-info":[{"award-number":["1180348"]}],"id":[{"id":"10.13039\/501100010751","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Molecules"],"abstract":"<jats:p>The competitiveness of the BF3 Lewis acid (LA) catalyzed polar Diels\u2013Alder (P-DA) and polar Alder-ene (P-AE) reactions of 2-methyl-1,3-butadiene, a diene possessing an allylic hydrogen, with formaldehyde has been studied within the Molecular Electron Density Theory (MEDT) at the MPWB1K\/6-311G(d,p) computational level. Coordination of BF3 LA to the oxygen of formaldehyde drastically accelerates both reactions given the high electrophilic character of the BF3:formaldehyde complex. As a consequence, these reactions present a very low activation enthalpy\u2014less than 2.2 kcal\u00b7mol\u22121\u2014thus becoming competitive. In dioxane, the P-AE reaction is slightly favored because of the larger polar character of the corresponding transition state structure (TS). In addition, the Prins reaction between hexahydrophenanthrene and the BF3:formaldehyde complex has also been studied as a computational model of an experimental P-AE reaction. For this LA-catalyzed reaction, the P-DA reaction presents very high activation energy because of the aromatic character of the dienic framework. The present MEDT study allows establishing the similarity of the TSs associated with the formation of the C\u2013C single bond in both reactions, as well as the competitiveness between P-AE and P-DA reactions when the diene substrate possesses at least one allylic hydrogen, thus making it necessary to be considered by experimentalists in highly polar processes. In this work, the term \u201cpseudocyclic selectivity\u201d is suggested to connote the selective formation of structural isomers through stereoisomeric pseudocyclic TSs.<\/jats:p>","DOI":"10.3390\/molecules23081913","type":"journal-article","created":{"date-parts":[[2018,8,1]],"date-time":"2018-08-01T03:10:01Z","timestamp":1533093001000},"page":"1913","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":17,"title":["A Molecular Electron Density Theory Study of the Competitiveness of Polar Diels\u2013Alder and Polar Alder-ene Reactions"],"prefix":"10.3390","volume":"23","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-2023-0108","authenticated-orcid":false,"given":"Luis R.","family":"Domingo","sequence":"first","affiliation":[{"name":"Department of Organic Chemistry, University of Valencia, Moliner 50, 46100 Valencia, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mar","family":"R\u00edos-Guti\u00e9rrez","sequence":"additional","affiliation":[{"name":"Department of Organic Chemistry, University of Valencia, Moliner 50, 46100 Valencia, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Patricia","family":"P\u00e9rez","sequence":"additional","affiliation":[{"name":"Facultad de Ciencias Exactas, Departamento de Ciencias Qu\u00edmicas, Universidad Andres Bello, Av. Rep\u00fablica 498, Santiago 8370146, Chile"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2018,7,31]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"98","DOI":"10.1002\/jlac.19284600106","article-title":"Synthesen in der hydroaromatischen Reihe","volume":"460","author":"Diels","year":"1928","journal-title":"Justus Liebigs Ann. Chem."},{"key":"ref_2","unstructured":"Carruthers, W. (1978). Some Modern Methods of Organic Synthesis, Cambridge University Press. [2nd ed.]."},{"key":"ref_3","unstructured":"Carruthers, W. (1990). Cycloaddition Reactions in Organic Synthesis, Pergamon Press."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"27","DOI":"10.1002\/cber.19430760105","article-title":"Absorption of maleic acid-anhydride and azodicarbon acid-ester in simple unsaturated carbohydrogens. 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