{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,24]],"date-time":"2026-09-24T02:16:42Z","timestamp":1790216202439,"version":"4.1.0"},"reference-count":79,"publisher":"MDPI AG","issue":"22","license":[{"start":{"date-parts":[[2021,11,14]],"date-time":"2021-11-14T00:00:00Z","timestamp":1636848000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100005995","name":"Bulgarian Academy of Sciences","doi-asserted-by":"publisher","award":["DFNP-144\/2016"],"award-info":[{"award-number":["DFNP-144\/2016"]}],"id":[{"id":"10.13039\/501100005995","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100005995","name":"Bulgarian Academy of Sciences","doi-asserted-by":"publisher","award":["DFNP-17-63\/2017"],"award-info":[{"award-number":["DFNP-17-63\/2017"]}],"id":[{"id":"10.13039\/501100005995","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100000780","name":"European Commission","doi-asserted-by":"publisher","award":["BG05M2OP001-1.002-0012"],"award-info":[{"award-number":["BG05M2OP001-1.002-0012"]}],"id":[{"id":"10.13039\/501100000780","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Molecules"],"abstract":"<jats:p>A series of squaric acid amides (synthesized in 66\u201399% isolated yields) and a set of chiral aminoalcohols were comparatively studied as ligands in a model reaction of reduction of \u03b1-chloroacetophenone with BH3\u2022SMe2. In all cases, the aminoalcohols demonstrated better efficiency (up to 94% ee), while only poor asymmetric induction was achieved with the corresponding squaramides. A mechanistic insight on the in situ formation and stability at room temperature of intermediates generated from ligands and borane as possible precursors of the oxazaborolidine-based catalytic system has been obtained by 1H DOSY and multinuclear 1D and 2D (1H, 10\/11B, 13C, 15N) NMR spectroscopy of equimolar mixtures of borane and selected ligands. These results contribute to better understanding the complexity of the processes occurring in the reaction mixture prior to the possible oxazaborolidine formation, which play a crucial role on the degree of enantioselectivity achieved in the borane reduction of \u03b1-chloroacetophenone.<\/jats:p>","DOI":"10.3390\/molecules26226865","type":"journal-article","created":{"date-parts":[[2021,11,14]],"date-time":"2021-11-14T20:51:53Z","timestamp":1636923113000},"page":"6865","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":10,"title":["Chiral Aminoalcohols and Squaric Acid Amides as Ligands for Asymmetric Borane Reduction of Ketones: Insight to In Situ Formed Catalytic System by DOSY and Multinuclear NMR Experiments"],"prefix":"10.3390","volume":"26","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-0164-8453","authenticated-orcid":false,"given":"Yana","family":"Nikolova","sequence":"first","affiliation":[{"name":"Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Bl. 9, Acad. G. Bonchev Str., 1113 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0437-2162","authenticated-orcid":false,"given":"Georgi M.","family":"Dobrikov","sequence":"additional","affiliation":[{"name":"Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Bl. 9, Acad. G. Bonchev Str., 1113 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Zhanina","family":"Petkova","sequence":"additional","affiliation":[{"name":"Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Bl. 9, Acad. G. Bonchev Str., 1113 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Pavletta","family":"Shestakova","sequence":"additional","affiliation":[{"name":"Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Bl. 9, Acad. G. Bonchev Str., 1113 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2021,11,14]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"63","DOI":"10.1002\/chir.22268","article-title":"Synthesis of Single-enantiomer Bioactive Molecules: A Brief Overview","volume":"26","author":"Abdul","year":"2014","journal-title":"Chirality"},{"key":"ref_2","unstructured":"Lin, G., Li, Y., and Chan, A.S.C. (2002). Asymmetric Catalytic Hydrogenation and Other Reduction Reactions. Principles and Applications of Asymmetric Synthesis, John Wiley & Sons, Inc."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"569","DOI":"10.1021\/acscombsci.6b00050","article-title":"Efficient Routes to a Diverse Array of Amino Alcohol-Derived Chiral Fragments","volume":"18","author":"Haftchenary","year":"2016","journal-title":"ACS Comb. 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