The Phosphinoboration of N‐Heterocycles

The Phosphinoboration of N‐Heterocycles

The addition of phosphinoboronate ester Ph2PBpin (pin=1,2‐O2C2Me4) (1) to a number of different N‐heterocycles has been investigated. Reaction of 1 with pyridine resulted in highly selective formation of the corresponding 1,4‐addition product, with addition of the electron‐deficient Bpin group to th...

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Bibliographic Details
Published in:Chemistry : a European journal Vol. 23; no. 58; pp. 14485 - 14499
Main Authors: Geier, Stephen J., Vogels, Christopher M., Mellonie, Niall R., Daley, Erika N., Decken, Andreas, Doherty, Simon, Westcott, Stephen A.
Format: Journal Article
Language:English
Published: Germany Wiley Subscription Services, Inc 17-10-2017
Subjects:
Boron
boronium
Chemistry
Computer applications
dearomatization
Nitrogen
phosphines
phosphinoboration
Pyridines
Quinoline
phosphines
boronium
pyridines
phosphinoboration
dearomatization
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Summary:The addition of phosphinoboronate ester Ph2PBpin (pin=1,2‐O2C2Me4) (1) to a number of different N‐heterocycles has been investigated. Reaction of 1 with pyridine resulted in highly selective formation of the corresponding 1,4‐addition product, with addition of the electron‐deficient Bpin group to the pyridine nitrogen atom and the phosphido group to the para carbon atom. Conversely, reactions of para‐substituted pyridine derivatives occurred predominately to afford 1,2‐addition products while quinoline reacted to afford the 1,2‐adduct which ultimately isomerized to afford the corresponding 1,4‐addition product. Preliminary computational studies have been undertaken to explore possible pathways for these transformations including transfer of the PPh2− anion from [B(PPh2)2pin]− to the 4‐position of a borenium/boronium activated pyridine and concerted pathways for 1,2‐addition via intramolecular nucleophilic attack of PPh2 at C2 of a Ph2PBpin‐coordinated pyridine via a four‐centered transition state and intramolecular transfer of PPh2 to the 2‐position of a boron‐activated pyridine in a phosphido‐bridged dimer involving a six‐centered transition state. Do you like Piña colato? The addition of Ph2PBpin (1, pin=pinacolato, O2C2Me4) to a variety of pyridine derivatives and benzofused N‐heterocycles results in 1,2‐ and/or 1,4‐addition depending upon the nature of the substrate. Borenium/boronium cation intermediates are implicated in reactions using polar solvents that afford 1,4‐addition products.
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ISSN:0947-6539
1521-3765
DOI:10.1002/chem.201702203