Ken Tsutsumi

Rh(I)-catalyzed CO gas-free carbonylative cyclization reactions of alkynes with 2-bromophenylboronic acids using formaldehyde.

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.

Synthesis and structure of cationic η3-allenyl/propargylpalladium complexes

Abstract Treatment of η 1 -allenyl- or η 1 -propargylpalladium bis(triphenylphosphine) chloride with AgBF 4 or NaBPh 4 afforded cationic η 3 -allenyl/propargylpalladium complexes. The molecular structure and some properties of the η 3 -allenyl/propargylpalladium were revealed.

A new route for the construction of the AB-ring core of Taxol

Abstract A new method for the construction of the AB-ring core of Taxol was developed utilizing a new skeletal transformation protocol as a pivotal step. The acid-catalyzed rearrangement of the cyclopentenone–allene photoadduct gave a bridged seven-membered ketone, which was easily transformed, using the intramolecular Suzuki reaction and the oxidative cleavage of the vicinal diol, to the bicyclic diketone.

Cross-coupling reactions proceeding through η1- and η3-propargyl/allenyl–palladium(II) intermediates

Abstract The efficiency of cross-coupling between propargyl electrophiles and organotin(IV) or zinc(II) compounds catalyzed by phosphine–palladium complexes has been examined as a function of PR3/Pd ratio, the nature of the organometallics, and the nature of the leaving group of the electrophile. The coupling between RCCCH2Cl and PhSnBu3 proceeded much more smoothly by use of a catalyst precursor having a PPh3/Pd ratio of 1/1 rather than 4/1, while the rate of the coupling using PhCCSnBu3, instead of PhSnBu3, was less sensitive to the PPh3/Pd ratio. The regiochemistry of the coupling (formation of alkyne or allene) was also sensitive to the PPh3/Pd ratio in the case of the reaction between RCCCH2Cl and PhZnCl, but was much less sensitive in the reaction using PhSnBu3. These results have been rationalized by a general mechanistic scheme involving not only η1-propargyl or η1-allenylpalladium(II) which was considered in previous studies but also η3-propargylpalladium(II) species as a new reactive intermediate candidate. The carbonates, RCCCH2OCOC2H5, failed to undergo as clean a cross-coupling as was found with the chlorides, but instead provided products arising from the coupling of two RCCCH2 units without any participation of organotin(IV) reagents.

Mutual isomerization of η1-allenyl and η1-propargyl complexes of platinum via a five-coordinate η3-allenyl/propargyl intermediate

The reversible spontaneous isomerization between η1-allenyl and η1-propargylplatinum complexes is reported, which is suggested to proceed via pseudorotation of a five-coordinate η3-allenyl/propargyl intermediate.

Mechanistic studies on mutual isomerization of propargyl- and allenylplatinum(II) complexes

Abstract When heated in benzene, phenyl-substituted propargylplatinum(II) complexes, trans -Pt(CH 2 CCPh) (X) (PPh 3 ) 2 , ( 2 ) (XCl, Br, I), isomerized gradually to the more stable allenyl isomers, trans -Pt(CPhCCH 2 )(X)(PPh 3 ) 2 ( 3 ), to give rise to an equilibrium mixture of 2/3 (5/95), from which 3 (XCl) was isolated as an isomerically pure sample. The allenyl complex 3 also gave rise to the same equilibrium mixture of 2/3 when heated under the same conditions. The rate of propargyl- to allenylplatinum(II) isomerization was examined as the function of the ligand X in 2 . The isomerization rate was first-order in the concentration of the propargyl complex, not affected by adding PPh 3 , and increased in the order X = Cl cis -Pt(CH 2 CCPh) (CCPh) (PPh 3 ) 2 , isomerized even faster to the corresponding allenyl isomer than 2 . These kinetic aspects led us to suggest that the spontaneous propargyl- to allenylplatinum isomerization proceeds via intramolecular rearrangement of an 18-electron η 3 -propargyl/allenyl intermediate, Pt(η 3 -CH 2 CCPh) (X) (PPh 3 ) 2 . The isomerization from 2 to 3 was accelerated considerably by addition of Pt(PPh 3 ) 2 L n (LPPh 3 , n = 2; LC 2 H 4 , n = 1), but not at all by addition of PtCl 2 (PPh 3 ) 2 .

Rhodium-catalyzed CO gas-free carbonylative cyclization using aldehydes

A new protocol for CO gas-free carbonylation, in which aldehydes are used as a substitute for CO, is described. The protocol consists of two Rh-mediated processes; the Rh-mediated decarbonylation of aldehydes, which leads to the formation of Rh carbonyl, and subsequent Rh-catalyzed carbonylative cyclization utilizing the in situ formed Rh carbonyl species.

Intermolecular propargyl/allenyl group transfer from Pd(II) to Pt(0) and Pt(II) to Pd(0). Key reaction in metal-catalyzed isomerization between propargyl and allenyl metal complexes

Isomerization of phenyl-substituted propargylplatinum(II) complex, trans-Pt(CH2CCPh)(Cl)(PPh3)2 (1) to allenyl complex, trans-Pt(CPhCCH2)(Cl)(PPh3)2 (2) was found to be catalyzed by zerovalent complex Pd(PPh3)4. The reaction was proposed to proceed through the transfer of the propargyl/allenyl ligand both from Pt(II) to Pd(0) and Pd(II) to Pt(0). The former transfer, which seemingly has a thermodynamic disadvantage, has unambiguously been confirmed to take place; treatment of 1 with Pd(PPh3)4 or a mixture of Pd2(dba)3 and PPh3 resulted in the formation of Pd(I) complex, Pd2(μ-PhCCCH2)(μ-Cl)(PPh3)2 which lies in equilibrium with a mixture of propargyl/allenylpalladium(II) and Pd(0) complexes.

Reductive radical cyclization of cyclic γ-cyanoketones promoted by samarium(II) iodide without photoirradiation

Abstract Reaction of cyclic γ-cyanoketones with 3 equiv. of SmI 2 in the presence of t -BuOH as a proton source in HMPA–THF without photoirradiation gave the desired α-hydroxycycloalkanones along with overreduced ketones after hydrolysis. In the absence of t -BuOH, the formation of the overreduced ketones was depressed and the yields of the α-hydroxyketones increased, while the reaction proceeded slowly.

Mechanism for degradation of poly(sodium acrylate) by bacterial consortium no. L7-98.

Poly(sodium acrylate) (PSA) can be degraded by consortia of several bacterial species. We investigated the degradation mechanism for PSA (average molecular weight, 2100) by consortium no. L7-98. PSA was used as the sole carbon source in a mineral salt medium. After cultivation, the PSA had a range of molecular weights, including low-molecular-weight compounds, which were purified by gel-permeation and reversed-phase column chromatography. One purified compound, B1, with the molecular weight of 200, had a carbonyl group next to the terminus, according to 1H and 13C nuclear magnetic resonance spectrometry and X-ray analysis of the crystal structure. Two categories of metabolites of PSA were detected in the culture by electrospray ionization mass spectrometry. Results of high-resolution mass spectrometry (HR-MS) suggested that one kind of compounds had a carbonyl group and that the other kind of compounds had an aldehyde group and a double bond. Compounds having the molecular weights of 200 and 272 were rapidly produced from an acrylic acid oligomer with the molecular weight of 258 by resting cells of the consortium. HR-MS showed that a methylene group at the terminal unit was oxidized to a carbonyl group and that the compound with the molecular weight of 200 was compound B1. From these results, we propose that the degradation pathway of PSA involves (i) oxidation of a methylene group to a carbonyl group next to the terminus, (ii) decarboxylation to form an aldehyde group and dehydrogenation to form a double bond between the terminal unit and the next unit, and (iii) oxidation of the aldehyde group to a carboxyl group followed by elimination of an acetic acid.