The role of liquid confinement on the asymmetric Rh catalysis was studied using the 1,2-addition of phenylboroxine (2)t oN-tosylimine 1 in the presence of [RhCl(C 2 H 4 ) 2 ] 2 and chiral dienel igandsa sb enchmark reaction. To get access to Rh complexes of differentpolarity,enantiomerically pure C 2 -symmetric p-substituted 3,6-diphenylbicyclo[3.3.0]octadienes 4 and diastereomerically enriched unsymmetric norbornadienes 5 and 6 carrying either the Evans or the SuperQuat auxiliary were synthesized.Amicroemulsion containing the equal amounts of H 2 O/KOH and toluene/reactants was formulated using the hydrophilic sugar surfactant n-octyl b-d-glucopyranoside( C 8 G 1 )t om ediate the miscibility between the nonpolarr eactants and KOH, neededt oa ctivate the Rh-diene complex. Prominent features of this organized reaction medium are its temperature insensitivity as well as the presence of water and toluenerich compartments with ad omain size of 55 confirmed by small-angle X-ray scattering (SAXS). Althoughb icyclooctadiene ligands 4a,b,e performed equally well under homogeneous and microemulsion conditions, ligands 4c,d gave a different chemoselectivity.F or norbornadienes 5, 6,h owever, microemulsions markedly improved conversion and enantioselectivity as well as reaction rate, as was confirmed by kinetic studies using ligand 5b.Scheme1.EnvisionedRh-catalyzed asymmetric 1,2-additions in the presence of novel chiral bicyclo[3.3.0]octadiene and norbornadiene basedl igands 4-6 (ME:microemulsion). Scheme2.Synthesis of novel chiral bicyclo[3.3.0.]octadiene ligands 4.For details see the SupportingInformation.

In order to study the impact of regioisomeric diene ligands on the formation and catalytic activity of Rh complexes, a series of C- and C-symmetric 2,5-disubstituted bicyclo[3.3.0]octa-2,5-dienes C-L and C-L, respectively, were synthesized from Weiss diketone by simultaneous deprotonation/electrophilic trapping of both oxo functions, and the catalytic behavior was studied in the presence of [RhCl(CH)]. Complexes [RhCl(C-L)] bearing C-symmetric ligands catalyzed effectively the asymmetric arylation of N-tosylaldimines to (S)-diarylamines with yields and ee values up to 99%. In Hayashi-Miyaura reactions, however, the complexes showed poor catalytic activity. When complexes [RhCl(C-L)] with C-symmetric ligand or mixtures of [RhCl(C-L)] and [RhCl(C-L)] were employed in 1,2-additions, racemic addition products were observed, suggesting a C═C isomerization of the diene ligands. X-ray crystal structure analysis of both Rh complexes formed from the [RhCl(CH)] precursor and ligands C-L and C-L revealed that only the C-symmetric ligand C-L coordinated to the Rh, whereas C-L underwent a Rh-catalyzed C═C isomerization to rac-C-L, which then gave the racemic [RhCl(rac-C-L)] complex. DFT calculations of the relative stabilities of the Rh complexes and the proposed intermediates provided a mechanistic rationale via Rh-mediated hydride transfer.

Improved reaction rate and enantioselectivity of Rh‐catalyzed asymmetric 1,2‐additions of phenylboroxine to N‐tosylimine was realized when the conventional solutions were replaced by microemulsions stabilized by hydrophilic sugar surfactants containing equal amounts of H2O/KOH and toluene/reactants. The norbornadiene ligands on the catalyst differ in the substitution pattern and oxazolidinone unit. For more information, see the Full Paper by T. Sottmann, S. Laschat and co‐workers on page 9464 ff.