Synthesis and structure of potential Lewis acid–Lewis base bifunctional catalysts: 1-N,N-dimethylamino-8-borononaphthalene derivatives

Synthesis and structure of potential Lewis acid–Lewis base bifunctional catalysts: 2-N,N-Diisopropylaminophenylboronate derivatives

“…It was possible to gather some evidence for formation of compound 10b in solution (acetonitrile), especially by 11 B NMR, which showed a clear, sharp triplet at d 3.68 (J 56.3 Hz). This is diagnostic [5] of both the difluoroborane function in 10 and the fact that there is strong B-N chelation according to the low chemical shift suggesting it exists as 10b rather than 10a.…”

“…Isolation of the boronic acid derivative 8a, allowed us to then investigate the formation of the corresponding difluoroborane 10, which we expected would be accessible from the trifluoroborate salt. Hence, reaction with potassium hydrogen difluoride provided the HF salt 9, rather than the potassium salt [8], or the neutral difluorborane 10, which can result when there is a basic function proximal to the boron centre [5]. In this case, both the basicity of the amino group and the appearance of a hydrogen bond between a fluorine atom and the N-H (see X-ray structure below), seem to work together to give preference for formation of the HF salt 9.…”

“…Indeed, one of the boronic acid functions prefers to form a relatively linear hydrogen-bond to the diisopropylamine nitrogen as part of an seven-membered ring, which is an extremely short H-bond of 2.637 Å (O1-H1-N1), compared to 2.861 Å which is the median value for such bonds according to the Cambridge Structural Database (CSD) [9]. The preference for hydrogen-bonding in both the solid and solution phases for the diisopropylbenzylamine derivative 8a vs. B-N chelation is in stark contrast to the corresponding dimethylbenzylamine derivative [5] which only exhibits B-N chelation in both solution and solid phases. This result suggests that steric hindrance alone may be sufficient to suppress the intramolecular B-N Table 1 Selected bond lengths and bond angles for structures 3 and 11 …”

“…The key factors in these studies have been the development of general methods for the synthesis of amino-boronic acid systems, and gaining an understand ing of the structural properties which contribute to different catalytic activities. To this end, we examined methods for the synthesis of and the resulting structural properties of 1,8-N,N 0 -dimethylaminonaphthaleneboronic acid [5], and found that in this system, B-N chelation is present in all the analogues prepared. In this paper, we report our further endeavours into the preparation of bifunctional amino-boronate derivatives based upon ortho-benzylamine boronic acid systems.…”

Asymmetric Direct Amide Synthesis by Kinetic Amine Resolution: A Chiral Bifunctional Aminoboronic Acid Catalyzed Reaction between a Racemic Amine and an Achiral Carboxylic Acid

“…[7] With these considerations in mind, we endeavored to develop a catalytic direct amide formation under mild conditions, though still well above room temperature. The current limiting temperature appears to be 85 8C, the temperature at which reactions can be carried out with bifunctional aminoboronic acid catalysts by using azeotropic water removal in fluorobenzene.[2] Although these reaction conditions are relatively mild compared to all other direct amide formation reactions with boron-derived catalyts, [4,5] they do not completely preclude the thermal direct amide formation with the more reactive carboxylic acid/amine combinations.[2] Though the prospect of developing asymmetric catalysts for amide formation may not look promising, [7] we report herein preliminary results that demonstrate asymmetric processes are possible under elevated temperatures with the development of a planar chiral ferrocenederived bifunctional aminoboronic acid catalyst.Our recent interests in the development of bifunctional aminoboronic acids as potential catalysts [8] led to the development of N,N-di-iso-propylbenzylaminoboronic acid type catalysts [2] such as commercially available 1 and planar chiral ferrocene analogue 2. We recently reported using a (À)-sparteine-directed metallation to provide 2 in 96 % ee.…”