Despite the economic and environmental merits of iron, organoiron species is largely underused for catalysis, mainly because of the difficulty in controlling its reactivity. In this account, I describe our efforts toward controlling the reactivity of transient organoiron species and its utilization for catalytic C-H bond activation. The design of an organoiron species stabilized by a bidentate directing group and a diphosphine ligand, its applications to the catalytic reaction of carboxamides with organometallic reagents or with electrophiles, and a recent iron catalyst stabilized by a triphosphine ligand capable of activating the C-H bond of weakly coordinating carbonyl compounds are described.
The palladium-catalyzed direct arylation polymerization (DArP) has recently emerged as a viable alternative to the existing synthetic means of π-conjugated polymers based on cross-coupling reactions. DArP has a distinct advantage over cross-coupling polymerization in the synthesis of donor-acceptor type alternating copolymers (DA polymers), which have proven to be a competent component of optoelectronic devices such as organic solar cells and field effect transistors. So far, DA polymers have been prepared by Migita-Stille cross-coupling polymerization. However, this method needs toxic tin reagents for monomer preparation. Moreover, the polymerization reaction forms a highly toxic side product such as Me3SnBr. It is expected that the DArP process, which proceeds via C-H bond activation, would provide a fundamental solution for these problems.
We have newly designed N-aryl oxindole with C-N axial chirality as a common intermediate for diastereoselective and divergent synthesis of a variety of 3,3-disubstituted oxindoles bearing a C3 stereogenic center. High diastereoselectivities (up to >95:<5) were observed with ortho-monosubstituted N-aryl oxindole systems through transformations including nucleophilic addition, alkylation, and cycloaddition. Facile removal of the p-(benzyloxy)aryl moiety in axially twisted amides was achieved by a mild, two-step sequence. We also describe the first synthesis of an enantiomerically pure C-N axially chiral N-aryl isatin from the corresponding N-aryl oxindole, which was synthesized by an asymmetric intramolecular Buchwald-Hartwig N-arylation.
In 2004 we reported an anti-selective remote asymmetric induction reaction using chiral vinylketene silyl N,O-acetal 1 (the stereoselective vinylogous Mukaiyama aldol reaction). The reaction has been applied to natural product synthesis by many groups since the reaction makes syntheses short and efficient by simultaneous introduction of both asymmetric centers and the multiply functionalized carbon chain. Recently, we have developed a variety of remote asymmetric induction reactions using the E,E-vinylketene N,O-acetal 1. Additionally, we have developed a new strategy to synthesize polypropionates in short steps by combining remote asymmetric induction reactions and functionalization of double bonds. In this paper, the new strategy as well as new remote asymmetric induction reactions and their applications to syntheses of polypropionates are described.
The intramolecular aryl-aryl coupling reaction of phenyl benzoate derivatives is a convenient method for construction of a 6H-dibenzo [b,d] pyran-6-one skeleton which is frequently found in natural products. Palladium reagents are used for the C-C bond formation between two aromatic rings. This review article describes that this technique is effective for the syntheses of several natural products possessing a highly oxygenated 6H-dibenzo [b,d] pyran-6-one core. The regioselectivity in the reaction is also discussed with some transition state illustrations. For further application, asymmetric construction of the biphenyl moiety is presented using the dynamic kinetic optical resolution method.
In the latter part, the biphenyl synthesis and the diphenyl ether synthesis under the Ullmann conditions are described toward the total synthesis of ellagitannins. The syntheses of several important part structures of ellagitannins are illustrated using the Ullmann reactions. Finally, one example of the total synthesis of ellagitannin is demonstrated.
Catalytic cleavage and reconnection of carbon-carbon bond is a powerful tool for organic synthesis. Recently, activation of inert carbon-carbon bonds has been rapidly developed. This review summarizes the progress of catalytic activation of carbon-carbon bonds in cyclopentanone derivatives.