The rational design and development of novel transitionmetal catalysts bearing diolefin [1,2] and phosphine-olefin ligands [3] has recently gained attention for the promotion of catalytic enantioselective reactions such as conjugate and imine additions, as well as the cyclization of ynals. [4] The heteroleptic complexes generated from phosphine-alkene ligands can be particularly useful as they include at least two donors with distinct steric and electronic properties. Phosphine-alkene ligands featuring dibenzo[b,f]azepine [5] motifs have previously been reported in enantioselective allylic displacement [3j, 6] and conjugate addition [7] reactions. As the exploration of these and related ligand types continues to evolve, their use in novel processes will increase. Herein, we report an asymmetric intramolecular Rh-catalyzed hydroacylation [8] reaction of pent-4-enals for the preparation of cyclopentanones [Eq. (1)]. Two key features of the catalytic system are noteworthy: this is the first time phosphoramiditealkene ligands have been used for this reaction type and the incorporation of an achiral phosphine coligand is necessary to promote enantioselective catalysis.After the seminal report in 1972 [9] by Sakai et al., in which stoichiometric Rh I was used, Miller and co-workers [10] and Larock et al. [11] showed that substituted g-pentenals undergo hydroacylative cycloisomerization using [Rh(PPh 3 ) 3 Cl]. Their protocol featured solvent saturated with ethylene and necessitated high catalyst loading (up to 50 mol %); additionally, they noted the formation of considerable amounts of side products from competitive decarbonylation pathways. Bosnich and co-workers [12] and Sakai et al. [13] independently reported catalytic enantioselective intramolecular hydroacylation with cationic rhodium perchlorate catalysts prepared from binap or Me-DuPhos. [14] These studies showed that to obtain good product selectivity the matching of the diphosphine ligand to the pentenal substrates was of the utmost importance. Subsequent investigations with isotopic labelling have also been undertaken to shed light on the mechanistic details. [10,15] It has been suggested that the benefits of ethylene in the reaction mixture, mentioned in the early reports, arise from the formation of a coordinatively saturated cationic rhodium species stabilized against decomposition. [10,11] This aspect of using ethylene piqued our interest and led us to examine the use of donor ligands incorporating an olefin. Additionally, we envisioned the implementation of combinatorial catalysis [16] involving heteroleptic complexes generated in situ, an approach that is highly rewarding as illustrated by the observations of Reetz et al., [17] Shibasaki and co-workers, [18] and Ding and co-workers. [19] In prospecting experiments we examined pentenal 1 a, as the prototypical substrate, under various reaction conditions with complexes generated in situ from [{RhCl(C 2 H 4 ) 2 } 2 ] and phosphoramidite ligands (S)-L1 [6] and (R,R,R)-L2 [20] in the presence of Ag I (T...
