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The quinine-thiourea provided the products possessing an \u03b1-quaternary chiral center in high enantioselectivities only in the case of electron rich enones. On the other hand, the quinine-squaramide was more efficient in that a wide variety of electron rich and electron poor enones underwent Michael addition of nitrophosphonates to afford the quaternary \u03b1-nitrophosphonates in excellent yields and enantioselectivities. The hydrogen bonding donor ability of the bifunctional catalyst, as shown in the proposed transition states, appears primarily responsible for the observed selectivity. However, a favorable \u03c0-stacking between the aryl groups of thiourea\/squaramide and aryl vinyl ketone also appeared favorable. The reaction was amenable to scale up, and the enantioenriched quaternary \u03b1-nitrophosphonates could be easily transformed to synthetically and biologically useful quaternary \u03b1-aminophosphonates and other multifunctional molecules.<\/jats:p>","DOI":"10.1021\/jo502332r","type":"journal-article","created":{"date-parts":[[2015,1,8]],"date-time":"2015-01-08T13:58:49Z","timestamp":1420725529000},"page":"1402-1413","source":"Crossref","is-referenced-by-count":35,"title":["Quinine-Derived Thiourea and\nSquaramide Catalyzed\nConjugate Addition of \u03b1-Nitrophosphonates to Enones:\nAsymmetric Synthesis of Quaternary \u03b1-Aminophosphonates"],"prefix":"10.1021","volume":"80","author":[{"given":"Kalisankar","family":"Bera","sequence":"first","affiliation":[{"name":"Indian Institute of Technology Bombay , , ,","place":["Mumbai, India, 400 076"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Irishi N. 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Chem."},{"key":"2026090218384061500_cit23b","first-page":"450","volume":"16","author":"Li","year":"2010","journal-title":"Chem.\u2500Eur. J."},{"key":"2026090218384061500_cit23c","doi-asserted-by":"crossref","first-page":"1724","DOI":"10.1021\/ol300307c","volume":"14","author":"Jakab","year":"2012","journal-title":"Org. Lett."},{"key":"2026090218384061500_cit23d","unstructured":"(d)\n          \n          The pKa in DMSO of the vinyl (instead of ethyl) analogue\nof thiourea C9 is reported to be 16.2, whereas that of C4 is reported to be 13.2 (ref 23b)."},{"key":"2026090218384061500_cit24a","doi-asserted-by":"crossref","first-page":"14416","DOI":"10.1021\/ja805693p","volume":"130","author":"Malerich","year":"2008","journal-title":"J. Am. Chem. Soc."},{"key":"2026090218384061500_cit24b","unstructured":"(b)\n          \n          Review: ref 22g and the references cited\ntherein. For studies on the H-bonding ability of various squaramide\ncatalysts:"},{"key":"2026090218384061500_cit24c","doi-asserted-by":"crossref","first-page":"1786","DOI":"10.1021\/ol5005017","volume":"16","author":"Ni","year":"2014","journal-title":"Org.\nLett."},{"key":"2026090218384061500_cit24d","unstructured":"(d)\n          \n          The pKa in DMSO of squaramide C16 is\n10.54 (ref 24c),\nwhereas the corresponding thiourea derivative C4 has\na pKa of 12.4 (ref 23c). The pKa\u2019s reported for C4 in refs 23b and 23c are slightly different\n(13.2 and 12.4, respectively)."},{"key":"2026090218384061500_cit25","doi-asserted-by":"crossref","first-page":"1967","DOI":"10.1021\/ol050431s","volume":"7","author":"Vakulya","year":"2005","journal-title":"Org. Lett."},{"key":"2026090218384061500_cit26","doi-asserted-by":"crossref","first-page":"2901","DOI":"10.1021\/ol060481c","volume":"8","author":"Cao","year":"2006","journal-title":"Org. 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Catal."}],"container-title":["The Journal of Organic Chemistry"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/pubs.acs.org\/doi\/pdf\/10.1021\/jo502332r","content-type":"application\/pdf","content-version":"vor","intended-application":"unspecified"},{"URL":"https:\/\/pubs.acs.org\/joceah\/article-pdf\/80\/3\/1402\/13795925\/jo502332r.pdf","content-type":"application\/pdf","content-version":"vor","intended-application":"syndication"},{"URL":"https:\/\/pubs.acs.org\/joceah\/article-pdf\/80\/3\/1402\/13795925\/jo502332r.pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,9,2]],"date-time":"2026-09-02T22:39:00Z","timestamp":1788388740000},"score":1,"resource":{"primary":{"URL":"https:\/\/pubs.acs.org\/joceah\/article\/80\/3\/1402\/1348856\/Quinine-Derived-Thiourea-and-Squaramide-Catalyzed"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2015,1,8]]},"references-count":115,"journal-issue":{"issue":"3","published-online":{"date-parts":[[2015,1,8]]},"published-print":{"date-parts":[[2015,2,6]]}},"URL":"https:\/\/doi.org\/10.1021\/jo502332r","relation":{},"ISSN":["0022-3263","1520-6904"],"issn-type":[{"value":"0022-3263","type":"print"},{"value":"1520-6904","type":"electronic"}],"subject":[],"published":{"date-parts":[[2015,1,8]]}}}