Rhodium catalysts organocatalysts

Optimized reaction conditions call for the use of Wilkinson s catalyst in conjunction with the organocatalyst 2-amino-3-picoline (60) and a Br0nsted add. Jun and coworkers have demonstrated the effectiveness of this catalyst mixture for a number of reactions induding hydroacylation and C—H bond fundionalization [25]. Whereas, in most cases, the Lewis basic pyridyl nitrogen of the cocatalyst ads to dired the insertion of rhodium into a bond of interest, in this case the opposite is true - the pyridyl nitrogen direds the attack of cocatalyst onto an organorhodium spedes (Scheme 9.11). Hydroamination of the vinylidene complex 61 by 3-amino-2-picoline gives the chelated amino-carbene complex 62, which is in equilibrium with a-bound hydrido-rhodium tautomers 63 and 64. 

Early work by Tomioka and coworkers [39] described a two-component Michael/ aldol process to cyclopentenes. Furthermore, rhodium-assisted Michael/aldol processes to cyclopentanes and cyclohexanes have also been reported [40]. Later, a Michael addition reaction in combination with an adehyde a-alkylation reaction was reported for the highly stereoselective formation of y-nitroaldehydes 50 [41]. In this publication, a series of aliphatic aldehydes 49 (at Rj) and ( )-5-iodo-l-nitropent-1-ene 48 were reacted in the presence of the organocatalyst 1 and benzoic acid in dimethyl sulfoxide (DMSO) to afford the resulting cyclopentene ring system 50 (Scheme 7.9). The diastereo- and enantioselective process follows the proposed mechanism beginning with enamine activation of the aldehyde to 51 by the catalyst 1 (blocking the re face), and Michael addition of 48 occurs at its more accessible si face. The full enamine-enamine mechanism, illustrated in Scheme 7.9, provided... 

The relay catalysis combining a mechanistically distinct transition metal catalyst and an organocatalyst for one cascade has stimulated intensive interest in recent years, as it could potentially enable highly efficient and/or unprecedented transformations in a one-pot operation. Indeed, excellent transformations have been established by this approach. One elegant example is relay catalysis using a rhodium complex/chiral Brpnsted acid binary system (Scheme 5.87) [88]. It is believed that the first catalytic... 

---