Progress in organometallic catalysis began with the discovery of the Roelen reaction (hydroformylation with carbon monoxide and hydrogen) in 1938 and the Reppe reaction (hydrocarboxylation with carbon monoxide and water) in 1939. Since then, carbonylation chemistry by using carbon monoxide has occupied a central position in organometallic chemistry, as it relates to organic synthesis. There is, however, the problem of using gaseous carbon monoxide (a toxic greenhouse gas) in this chemistry. Recently, some strategies that address this issue have appeared. This minireview describes carbonylation reactions that can be conducted without the direct use of carbon monoxide. These carbonylation reactions provide reliable and accessible tools for synthetic organic chemists.

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The reaction of enynes with aldehydes in the presence of a catalytic amount of [RhCl(cod)](2)/dppp results in the Pauson-Khand-type reaction without the use of gaseous carbon monoxide to give bicyclic cyclopentenones in high yields (14 examples). Aldehydes serve as a source of carbon monoxide, and their carbonyl moiety is transferred to enynes, resulting in the formation of the carbonylated products. This reaction represents the first example of a CO-transfer carbonylation.

The rhodium(I)-catalyzed reaction of alkynes with 2-bromophenylboronic acids in the presence of paraformaldehyde resulted in a CO gas-free carbonylative cyclization, yielding indenone derivatives. [RhCl(BINAP)](2) and [RhCl(cod)](2) were responsible for the decarbonylation of formaldehyde and the subsequent carbonylation of alkynes with 2-haloboronic acids, respectively, leading to efficient whole carbonylation. Sterically bulky and electron-withdrawing groups on unsymmetrically substituted alkynes favored the alpha-position of indenones.

The development of new, efficient methods for the construction of ring systems from simple acyclic building blocks represents an important ongoing challenge for synthetic organic chemists. 1 One of the most extensively studied, recent approaches involves the transition-metalcatalyzed cycloisomerization of enynes. 2 A variety of such reactions have been developed thus far, and they can be classified into several types, depending on the type of transformation: (1) to cyclopentane derivatives containing an exo 1,3-or 1,4-diene unit, 3 (2) to bicyclo[4.2.0]-octene derivatives via a [2 + 2] cycloaddition, 4 (3) to bicyclo[4.1.0]heptene derivatives, 5 (4) to seven-membered cyclic alkenes, 6 (5) to eight-membered cyclic dienylsilane, 7 and (6) to 1-vinylcycloalkenes via skeletal reorganization. 8,9 The reaction course is complicated and depends on reaction variables, such as the structure of the substrates, the nature of the catalysts, additives, solvents, and as well as others. Because of these variables, it is clear that the examination of a variety of substrates and catalyst type is of important in terms of finding new types of cycloisomerization reactions of enynes. Although a variety of transition metals have been examined for their ability to catalyze cycloisomerizations, the Ircatalyzed cycloisomerization of enynes has not been comprehensively examined. Recently, we found that simple transition-metal halides, such as [RuCl 2 (CO) 3 ] 2 and PtCl 2 , serve as effective catalysts for the skeletal reorganization of enynes to 1-vinylcycloalkenes in high product yields and a high selectivity (>98% isomeric purity in all cases). 9a,b,10 A characteristic feature of these catalytic systems is that they can be used with the enynes having a terminal acetylenic moiety. The latter are not suitable substrates for the other catalytic systems reported to date. 8 In the case of Ru(II) and Pt(II) catalyst systems, only skeletal reorganization occurred, and other types of cycloisomerization were not detected. In contrast, it was found that the reaction pattern for the Ir(I)-catalyzed reaction of enynes depends on both the structure of substrates and the nature of catalyst systems used. We wish to report herein on the Ir-catalyzed cycloisomerization of 1,6-and 1,7-enynes.The reaction of 1,6-enyne 1 was carried out under both CO and N 2 , because we had previously observed that the presence of a CO ligand on the metal in the Ru(II)-catalyzed reaction appears to be effective in allowing the reaction to proceed. 9a The treatment of 1,6-enyne 1 with 4 mol % [IrCl(CO) 3 ] n in toluene at 80°C under an atmosphere of CO gave a skeletal reorganization product, 3-ethenyl-3-cyclopentene-1,1-dicarboxylic acid diethyl ester (2), in 50% isolated yield (eq 1). The reaction was slow, and 2 days were required to complete the reaction. No byproducts were detected by GC and NMR, although the starting substrate 1 was completely consumed. 11 The reaction was more effective when conducted in an atmo- † Rodríguez, D. C.; Dérien, S.; Dixneuf, P. H. Synle...

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We previously showed that curcumin, a phytopolyphenol found in turmeric (Curcuma longa), targets a series of enzymes in the ROS metabolic pathway, induces irreversible growth arrest, and causes apoptosis. In this study, we tested Pentagamavunon-1 (PGV-1), a molecule related to curcumin, for its inhibitory activity on tumor cells in vitro and in vivo. PGV-1 exhibited 60 times lower GI50 compared to that of curcumin in K562 cells, and inhibited the proliferation of cell lines derived from leukemia, breast adenocarcinoma, cervical cancer, uterine cancer, and pancreatic cancer. The inhibition of growth by PGV-1 remained after its removal from the medium, which suggests that PGV-1 irreversibly prevents proliferation. PGV-1 specifically induced prometaphase arrest in the M phase of the cell cycle, and efficiently induced cell senescence and cell death by increasing intracellular ROS levels through inhibition of ROS-metabolic enzymes. In a xenograft mouse model, PGV-1 had marked anti-tumor activity with little side effects by oral administration, whereas curcumin rarely inhibited tumor formation by this administration. Therefore, PGV-1 is a potential therapeutic to induce tumor cell apoptosis with few side effects and low risk of relapse.

The skeletal reorganization of 1,6- and 1,7-enynes leading to 1-vinylcycloalkenes using Rh(II) as a catalyst is reported. Two possible isomers of 1-vinylcycloalkenes, type I and type II, can be obtained, the ratio of which are highly dependent on the substitution pattern of the enynes used. Formation of type I compounds involves a single cleavage of a C-C double bond, the product of which is identical to that of enyne metathesis. In contrast, the formation of type II compounds involves the double cleavage of both the C-C double and triple bonds, which has an anomalous bond connection. The presence of both a phenyl group at the alkyne carbon and a methyl group at the internal alkene carbon facilitates the formation of type II compounds. The electronic and steric nature of the substituents on the aromatic ring also affects the ratio of type I and type II. The nature of a tether also has a significant effect on the course of the reaction. Experimental evidence for the intermediacy of a cyclopropyl rhodium carbenoid, a key intermediate in the skeletal reorganization of enynes, is also reported. In addition to the skeletal reorganization of enynes, Rh(II) complexes were found to have a high catalytic activity for some cycloisomerization reactions of alkyne derivatives, including the bicyclization of enynes to bicyclo[4.1.0]heptene derivatives and the cyclization of alkynylfurans to phenol derivatives.