Phosphine-boronates: efficient bifunctional organocatalysts for Michael addition

Abstract

Phosphine-boronates R(2)P(o-C(6)H(4))B(OR')(2) have been evaluated as bifunctional organocatalysts for the Michael addition of malonate pronucleophiles to methylvinylketone. The presence of the Lewis acidic boron center adjacent to phosphorus significantly improves catalytic performance. Isolation and complete characterization of a key intermediate, namely a β-phosphonium enolate, substantiate the role of the Lewis acidic moiety in the catalytic process.

Design principles in frustrated Lewis pair catalysis for the functionalization of carbon dioxide and heterocycles

“…It was found, however, that phosphine-borane 1-Ph2P-2-Bcat-C6H4 (7) was also generated in the reaction conditions (Scheme 6). This family of phosphinoboranes is well known and several derivatives were previously reported by Bourissou and coworkers [39][40]. The independent synthesis of 7 did show that this species does not react with CO2 nor with catecholborane (Scheme 7).…”

Chiral Phosphine Catalyzed Asymmetric Michael Addition of Oxindoles

“…[6] Recently, the utilization of Brønsted basicity of the zwitterionic intermediates in mechanistically relevant g-additions has drawn much attention. [7] In sharp contrast, very little attention was paid to the conceptually simple Michael addition; only a few sporadic examples were reported, [8] despite the fact that such transformations are synthetically extremely useful. [9] To the best of our knowledge, there is no report on an asymmetric Michael addition mediated by a chiral phosphine (Scheme 1).…”

Designing Metal‐Free Frustrated Lewis Pairs Catalyst for the Efficient Dehydrogenation of Ammonia Borane

“…Moreover, for a FLP to easily dehydrogenate AB and to release H 2 (a reverse process of H 2 activation) it should have a proper distance between the acidic and basic centers. The short ortho ‐phenylene linker appears to enhance the acid–base cooperativity in dihydrogen activation with a proper B−D distance . A suitable M should be able to remove the protic (N−H) and hydridic (B−H) hydrogen atoms of AB to form AOB and zwitterionic M_H 2 (process S1 as shown in Scheme ) with a fairly low , .…”

“…The short ortho-phenylene linker appears to enhance the acid-base cooperativity in dihydrogen activation with ap roperB ÀDd istance. [33][34][35][36][37] As uitable M should be able to remove the protic (NÀH) and hydridic (BÀH) hydrogen atoms of AB to form AOB and zwitterionic M_H 2 (process S1 as shown in Scheme 1) with af airly low DG°, DG 6 ¼ 1 .I tis also expected that M_H 2 should release H 2 (process S2 as shown in Scheme 1) with al ow DG°, DG°2 and an egative DG, DG 2 ,s ot hat this step is both kinetically and thermodynamically feasible at room temperature. Because the dehydrogenation product of AB by M, AOB,h as both aBc enter and an Nc enter, AOB may bind to the basic centera nd acidic center of M,r espectively,t hrough ac yclic addition reaction( process S3 as shown in Scheme 1) to form M_AOB to poison M.T oa void this, either the DG°for S3 (DG°3 Þ,should be much higher than the DG°for the oligomerization of AOB,s ot hat AOB prefers oligomerization over S3, or the DG 6 ¼ forS 3s hould be positive if DG°3 is not high, so that the formation of M_AOB is thermodynamically infeasible.…”