The first examples of Rh-catalyzed cyclohydrocarbonylation-bicyclization of N-allylic amides of arylacetic acids are reported. This novel carbonylative bicyclization process was successfully applied to the rapid syntheses of crispine A and its analogues (tricyclic indolizidine alkaloids) as well as harmicine (tetracyclic beta-carboline alkaloid).
The prototype experimental example of "spontaneous" pattern formation in an unstirred chemical medium is the oscillatory Belousov-Zhabotinsky (BZ) reaction: target patterns of outward-moving concentric rings are readily observed when the reaction is run in a thin layer in a Petri dish. In many experimental runs, new target centers appeared to form closer to pre-existing target centers than expected in a randomized model. Here we describe a simple direct test for the presence of temporal order in the spatiotemporal dynamics of target nucleation, and apply this test to detect significant temporal order in target formation in the ferroin-catalyzed BZ reaction. We also describe how mixing heterogeneity can generate temporal order, even in the absence of heterogeneous physical nucleating centers.
The catalytic asymmetric conjugate addition to α , β -unsaturated compounds is one of the most powerful carbon -carbon and carbon -heteroatom bond -forming reactions in organic synthesis. The reaction is enormously useful for the construction of enantioenriched, highly functionalized carbon skeletons for the total syntheses of numerous biologically active compounds. The scope of the reaction is broad, owing to the availability of a large variety of donor and acceptor compounds. The high potential of this synthetic method is evident with the possibility of building multiple stereocenters in a single synthetic operation, and many asymmetric catalytic systems can exhibit high reactivity and stereoselectivity. In this chapter, recent advances in catalytic asymmetric conjugate addition reactions are described according to four categories: (i) conjugate addition of organometallics, (ii) conjugate addition of other carbon -centered nucleophiles, (iii) tandem conjugate addition reactions, and (iv) conjugate addition of heteroatom nucleophiles. 8A.2. CATALYTIC ASYMMETRIC CONJUGATE ADDITION OF ORGANOMETALLICSThe catalytic asymmetric conjugate addition of organometallic reagents to electrophilically activated olefi ns constitutes one of the most powerful methods for carbon -carbon Catalytic Asymmetric Synthesis, Third Edition, Edited by Iwao Ojima
The purpose of this research was to explore the unstirred, ferroin-catalyzed Belousov-Zhabotinsky (BZ) reaction as an experimental model for the response of excitable media to small perturbations (slightly larger than the threshold for excitations). Following Showalter et al. (Showalter, K.; Noyes, R. M.; Turner, H. J.Am. Chem. Soc. 1979, 101, 7463-69), we used a positively biased silver electrode to release silver ions into a BZ reaction mixture, removing bromide ions and causing an excitation if sufficient bromide was removed. We found (1) a scaling region in which the delay before activation increased linearly as the size of the perturbation decreased, qualitatively consistent with but not fully explained by the Oregonator of Field et al. (Field, R. J.; Körõs, E.; Noyes, R. M. J. Am. Chem. Soc. 1972, 94, 8649-64); (2) evidence for a 10 s oligomerization time scale; and (3) that activations were always delayed until after the end of a pulse of current, with the delay essentially constant for sufficiently long pulses, an effect not seen in simple ODE models but consistent with the anomalously large current apparently required for activation (Showalter, K.; Noyes, R. M. J. Am. Chem. Soc. 1976, 98, 3730-31) and explainable by bromide transport. Overall, the BZ system appeared to be well-suited as an experimental prototype, despite its complexity.
Development of highly efficient catalytic processes for the synthesis of natural and unnatural compounds of medicinal interest or useful as intermediates for functional materials is a central focus in modern organic synthesis. One of the most efficient approaches to such methodology developments is to apply transition‐metal catalyzed cyclization reactions for the transformations of simple starting materials into monocyclic, bicyclic, and polycyclic scaffolds that can be further elaborated into specific targets. This article concisely summarizes recent advances in the cyclizations promoted by homogeneous catalysts, including various carbocyclizations, carbonylative carbocyclizations, cyclohydrocarbonylations, intramolecular hydrosilylations, and silylformations, compiling relevant references up to late 2008. Among these catalytic cyclization processes, the carbocyclization and carbonylative carbocyclization are extremely important and useful reactions for the syntheses of a variety of carbocyclic and heterocyclic compounds. Cascade carbocyclization is a powerful method, providing a rapid access to polycyclic skeletons in one step. Cyclohydrocarbonylation is another powerful catalytic cyclization process, which finds a host of applications in organic syntheses. Intramolecular hydrosilylations and silylformations also provide unique methods for a variety of organic syntheses. Accordingly, catalytic cyclization reactions not only serve as highly useful synthetic methods in laboratories but also have high potential as future industrial processes.
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Alkaloids U 0600Efficient Syntheses of Crispine A and Harmicine by Rh-Catalyzed Cyclohydrocarbonylation. -Cyclohydrocarbonylation-bicyclization of N-allylic amides of arylacetic acids followed by reduction allows the preparation of crispine A (IVa), its analogues and tetracyclic β-carboline alkaloid harmicine (VII). -(CHIOU*, W.-H.; LIN, G.-H.; HSU, C.-C.; CHATERPAUL, S.
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