Allylboronic acids are synthetically very useful building blocks for chemical transformations. Due to their instability under ambient condition, the synthetic utility of allylboronic acids was not known broadly. Recently we reported that allylboronic acids react with wide range of carbonyl compounds without any additives.1,2 As part of our studies now we have demonstrated that, allylboronic acids react with imines and indoles under very mild conditions in absence of additive. The reactions proceed under mild conditions to afford high regio- and stereoselective homoallylic amines. Studies revealed that the selectivity of homoallylic amine does not depend on the geometry of starting imine. We observed anti selectivity for both E and Z imines. Experimental and theoretical studies shows, E-imine isomerize to Z-imine prior to allylation and this isomerization facilitated by the allylboroxine that formed in the dry reaction conditions. As the allylboroxine are extremely oxygen sensitive we treated arylboroxine (2  ) with pure E-imine (1  ) and observed the new imine species (3 ) (Scheme 1).Scheme1  . E/Z isomerization of imine (1  ) in the presence of aryl boroxine (Ar = 4-fluorophenyl). The major 1H dNOE is indicated for the two observed isomeric forms.NMR studies shows that the new species is Z-isomer of starting imine (1  ).3 This indicates that prior to allylation, imine 1  isomerize and afford anti selective homoallylic amine most likely via Zimmerman-Traxler chair type transition state. Computational studies also support that allylation of Z imine via chair type transition state follow the lowest activation barrier.3References: (1) Raducan, M.; Alam, R.; Szab�, K. J. Angew. Chem. Int. Ed. 2012  , 51, 13050.(2) Alam, R.; Raducan, M.; Eriksson, L.; Szab�, K. J. Org. Lett. 2013  , 15, 2546.(3) Szabo, K. J.; Alam, R.; Das, A.; Huang, G.; Eriksson, L.; Himo, F. Chem. Sci. 2014  .

Selective allylation of imines by allylboronic acids: Experimental and computational studies

248th National Meeting (2014)

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