Abstract

Abstract

Abstract

Abstract

Abstract

Abstract

Abstract

Abstract

We have developed catalytic isomerizations of 5-alkynals to γ-alkynyl ketones and cyclopent-1-enyl ketones using [Rh{P(OPh)₃}₂]BF₄ as a catalyst. Cu(OTf)₂ and AgBF₄ are also effective catalysts for the formation of γ-alkynyl ketones. The substituents at the 4-positions in 5-alkynals play important roles in the selection of two different isomerization pathways. The first catalytic endo/trans hydroacylation of acyclic 5-alkynals leading to cyclohexenones was also developed with [Rh(PPh₃)₂]BF₄ as a catalyst. Crossover deuterium-labeling studies indicated that these isomerization reactions proceed intramolecularly.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

The cover picture shows the cationic rhodium(I) complex catalyzed isomerization of 5-alkynals to four different types of ketones. The catalytic isomerization of 5-alkynals to δ-alkynyl ketones and cyclopent-1-enyl ketones proceeds by using Rh^I+/P(OPh)₃, whereas the catalytic endo/trans and exo/cis hydroacylation of 5-alkynals to cyclohexenones and cyclopentanones proceeds by using Rh^I+/PPh₃ and Rh^I+/BINAP, respectively. The ligands of the Rh catalysts and the substituents at the 4-position of the 5-alkynals play an important role in determining which isomerization product results. Details are discussed in the article by K. Tanaka et al. on p. 5675 ff.

We have determined that hydrogenated cationic Rh(I)/bisphosphane complexes are highly active catalysts for the isomerization of secondary propargylic alcohols to α,β-enones. A kinetic resolution of secondary propargylic alcohols proceeded with moderate selectivity with [Rh((R)-BINAP)]OTf as a catalyst. Mechanistic studies revealed that the isomerization proceeds through intramolecular 1,3- and 1,2-hydrogen migration pathways. The isomerization of propargylic diol derivatives was also investigated, which revealed that 1,4-diketones, furans, and α,β-enones were obtained from 2-butyn-1,4-diol, 1-methoxy-2-butyn-4-ol, and 1-acetoxy-2-butyn-4-ol derivatives, respectively. Furthermore, chemoselectivity of the isomerization of an acetylenic diol was investigated, and preferential oxidation of a propargylic hydroxy group was observed.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Hoch substituierte Titelverbindungen werden effizient durch eine enantioselektive [2+2+2]-Cycloaddition mit einem kationischen Rh^I-H₈-Binap-Katalysator erhalten (siehe Schema). Leicht zugängliche Substrate, milde Reaktionsbedingungen, eine einfache Ausführung und eine hohe katalytische Aktivität charakterisieren dieses Verfahren. cod=1,5-Cyclooctadien; H₈-binap=2,2′-Bis(diphenylphosphanyl)-5,5′,6,6′,7,7′,8,8′-octahydro-1,1′-binaphthyl; Ts=p-Toluolsulfonyl.

Densely substituted title compounds can be obtained efficiently through an enantioselective [2+2+2] cycloaddition catalyzed by a cationic Rh^I/H₈-binap complex (see scheme). This method is highly practical in view of the ready access to substrates, mild reaction conditions, operational simplicity, and high catalytic activity. cod=1,5-cyclooctadiene; H₈-binap=2,2′-bis(diphenylphosphanyl)-5,5′,6,6′,7,7′,8,8′-octahydro-1,1′-binaphthyl; Ts=p-toluenesulfonyl.

Cross-cyclotrimerizations of ether-linked α,ω-diynes and dimethyl acetylenedicarboxylate in the presence of a catalytic amount of cationic rhodium(I)/H₈-BINAP complex give [7]–[21]polyether cyclophanes in good yield. [8]–[9]Ester cyclophanes were also synthesized from the corresponding α,ω-diynes. The ratio of para-, meta-, and orthocyclophanes depends on the length and the structure of the α,ω-diyne tether chain, whilst the effect of concentration on the yield of polyether cyclophanes appears to be small. X-ray analysis revealed that a single crystal of [15]metacyclophane 4g was the chiral form and that of [5.5]metacyclophane 4k the racemic form, due to an absence of ring flip in the crystals. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

We established that a cationic rhodium(I)/dppf or dppb complex catalyzes a regio- and diastereoselective intermolecular [4+2] carbocyclization of 5-trimethylsilyl-4-pentynals with electron-deficient alkenes leading to cyclohexanones. We also established that a cationic rhodium(I)/(R,R)-Walphos complex catalyzes a regio- and enantioselective intermolecular [4+2] carbocyclization of 5-substituted 4-pentynals and 2-alkynylbenzaldehydes with N,N-dialkylacrylamides leading to enantio-enriched cyclohexanones and tetralones, respectively. A single olefin isomer was produced in every carbocyclization. Regioselectivities of the alkene insertion depend on the alkenes used. Mechanistic study suggested that a key intermediate in this intermolecular [4+2] carbocyclization is a five-membered acylrhodium intermediate, formed by cis addition of the rhodium hydride to the metal-bound alkyne. This method serves as an attractive new route to highly functionalized cyclohexanones in view of the one-step access to 5-substituted 4-pentynals and 2-alkynylbenzaldehydes starting from readily available terminal alkynes.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Cationic rhodium(I)/modified-BINAP complexes catalyze a chemo- and regioselective [2+2+2] cycloaddition of a wide variety of alkynes and nitriles leading to highly functionalized pyridines under mild reaction conditions. The asymmetric variant of this reaction, enantioselective desymmetrization of substituted malononitriles, also proceeded to give enantio-enriched bicyclic pyridines which possess a tertiary or quaternary stereocenter. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Enantiomerenangereicherte 2-Alkylidenglutarimide und Cyclopentenone entstehen bei der parallelen kinetischen Racematspaltung von 3-substituierten 4-Alkinalen mit einem kationischen Rh^I/(S)-Segphos-Katalysatorsystem. Diese Methode bietet einen attraktiven Zugang zu den genannten Produkten, da 4-Alkinale aus einfach zugänglichen terminalen Alkinen in einem Schritt erhalten werden können.

Enantioenriched 2-alkylideneglutarimides and cyclopentenones are prepared by parallel kinetic resolution of 3-substituted 4-alkynals with a cationic Rh^I/(S)-segphos catalyst system. This is an attractive route to the above-mentioned products given the one-step access to 4-alkynals from readily available terminal alkynes.

Selektive Ringe: Ein kationischer Rh^I-(R,R)-Walphos-Komplex katalysiert die hoch regio- und enantioselektive intermolekulare [4+2]-Carbocyclisierung von 4-Alkinalen mit N,N-Dialkylacrylamiden zu Cyclohexanonen (siehe Schema). Die Methode bietet einen einstufigen Zugang zu 4-Alkinalen aus kommerziell erhältlichen Reagentien.

A highly regioselective intermolecular cyclotrimerization of terminal alkynes has been developed based on the use of the cationic rhodium(I)/DTBM-Segphos complex. This method can be applied to a variety of terminal alkynes to provide 1,2,4-trisubstituted benzenes in high yield and with high regioselectivity. A chemo- and regioselective intermolecular crossed-cyclotrimerization of dialkyl acetylenedicarboxylates with a variety of terminal alkynes has also been developed based on the use of the cationic rhodium(I)/H8-BINAP complex, furnishing 3,6-disubstituted phthalates in high yields. It constitutes a highly efficient new method for intermolecular crossed-cyclotrimerization of two different monoynes in terms of catalytic activity, chemo- and regioselectivity, scope of substrates, and ease of operation. The versatility of this new crossed-alkyne cyclotrimerization procedure is demonstrated through its application to one-step synthesis of a [6]metacyclophane and [7]–[12]paracyclophanes from the corresponding terminal α,ω-diynes. Mechanistic studies have revealed that the chemo- and regioselectivity of this crossed-alkyne cyclotrimerization are determined by the preferential formation of a specific rhodium metallacycle derived from a terminal alkyne and a dialkyl acetylenedicarboxylate.

Easy access to axially chiral phthalides that bear one or two oxymethylene functionalities is provided by an enantioselective cross alkyne cyclotrimerization in the presence of the cationic complex [Rh^I{(S)-H₈-binap}]⁺. The axial chirality is introduced during the formation of the benzene ring with high enantioselectivity.

A novel intramolecular hydroacylation of 5- and 6-alkynals leading to α-alkylidenecycloalkanones was accomplished by using cationic a rhodium(I)/BINAP complex. For all cyclizations described, a single (E)-olefin isomer was obtained. At elevated temperature, hydroacylation and double bond migration of 5- and 6-alkynals proceeded in a one-pot reaction to give cycloalkenones. An intramolecular hydroacylation of a 7-alkynal was unsuccessful. This method represents an attractive new route to highly functionalized α-alkylidenecycloalkanones and cycloalkenones.

Einen einfachen Zugang zu axial-chiralen Phthaliden mit ein oder zwei Oxymethylen-Funktionalitäten bietet eine enantioselektive Alkincyclotrimerisierung in Gegenwart des kationischen Komplexes [Rh^I{(S)-H₈-binap}]⁺. Die axiale Chiralität wird während der Bildung des Benzolrings mit hoher Enantioselektivität eingeführt.