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1‐Alkali‐metal‐2‐alkyl‐1,2‐dihydropyridines: Soluble Hydride Surrogates for Catalytic Dehydrogenative Coupling and Hydroboration Applications
Author(s) -
McLellan Ross,
Kennedy Alan R.,
Mulvey Robert E.,
Orr Samantha A.,
Robertson Stuart D.
Publication year - 2017
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201703609
Subject(s) - chemistry , hydroboration , hydride , lithium (medication) , alkyl , alkali metal , steric effects , solvent , pyridine , medicinal chemistry , toluene , catalysis , potassium , metal , organic chemistry , medicine , endocrinology
Equipped with excellent hydrocarbon solubility, the lithium hydride surrogate 1‐lithium‐2‐ tert ‐butyl‐1,2‐dihydropyridine ( 1t Li) functions as a precatalyst to convert Me 2 NH⋅BH 3 to [NMe 2 BH 2 ] 2 (89 % conversion) under competitive conditions (2.5 mol %, 60 h, 80 °C, toluene solvent) to that of previously reported LiN(SiMe 3 ) 2 . Sodium and potassium dihydropyridine congeners produce similar high yields of [NMe 2 BH 2 ] 2 but require longer times. Switching the solvent to pyridine induces a remarkable change in the dehydrocoupling product ratio, with (NMe 2 ) 2 BH favoured over [NMe 2 BH 2 ] 2 (e.g., 94 %:2 % for 1t Li). Demonstrating its versatility, precatalyst 1t Li was also successful in promoting hydroboration reactions between pinacolborane and a selection of aldehydes and ketones. Most reactions gave near quantitative conversion to the hydroborated products in 15 minutes, though sterically demanding carbonyl substrates require longer times. The mechanisms of these rare examples of Group 1 metal‐catalysed processes are discussed.