Developing Lithium Chemistry of 1, 2‐Dihydropyridines: From Kinetic Intermediates to Isolable Characterized Compounds. Issue 41 (31st August 2015)

• Record Type: Journal Article
• Authors: Armstrong, David R.; Harris, Catriona M. M.; Kennedy, Alan R.; Liggat, John J.; McLellan, Ross; Mulvey, Robert E.; Urquhart, Matthew D. T.; Robertson, Stuart D.
• Is Part Of: Chemistry. Volume 21:Issue 41(2015)
• Page Start: 14410
• Page End: 14420
• Publication Date: 2015-08-31
• Subjects: Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201501880
• Languages: English
• ISSNs: 0947-6539

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>Generally considered kinetic intermediates in addition reactions of alkyllithiums to pyridine, 1‐lithio‐2‐alkyl‐1, 2‐dihydropyridines have been rarely isolated or characterized. This study develops their "isolated" chemistry. By a unique stoichiometric (that is, 1:1, alkyllithium/pyridine ratios) synthetic approach using tridentate donors we show it is possible to stabilize and hence crystallize monomeric complexes where alkyl is <italic>tert</italic>‐butyl. Theoretical calculations probing the donor‐free parent <italic>tert</italic>‐butyl species reveal 12 energetically similar stereoisomers in two distinct cyclotrimeric (LiN)₃ conformations. NMR spectroscopy studies (including DOSY spectra) and thermal volatility analysis compare new <italic>sec</italic>‐butyl and <italic>iso</italic>‐butyl isomers showing the former is a hexane soluble efficient hydrolithiation agent converting benzophenone to lithium diphenylmethoxide. Emphasizing the criticalness of stoichiometry, reaction of <italic>n</italic>BuLi/Me₆TREN with two equivalents of pyridine results in non‐alkylated 1‐lithio‐1, 4‐dihydropyridine⋅Me₆TREN and 2‐<italic>n</italic>‐butylpyridine, implying mechanistically the kinetic 1, 2‐<italic>n‐</italic>butyl intermediate hydrolithiates the second pyridine.</p> </abstract>