11 research outputs found
Octahydrocyclopenta[c]pyridine Scaffold â Enantioselective Synthesis and Indole Annulation
An optically active hexahydrocyclopenta[c]pyridine derivative with quaternary stereocenter was prepared as a new heterocyclic scaffold. Key reaction was the Pdâcatalyzed asymmetric allylic alkylation of a piperidineâbased ÎČâoxoester, which proceeded in very good yield with high level of enantioselectivity (90â%, 95â% ee). The αâallyl moiety was transformed into a 1,4âdiketone by Pdâcatalyzed Wacker oxidation with molecular oxygen (89â%). This intermediate was cyclized in an intramolecular aldol reaction furnishing the cyclopentenone motif (86â%). Hydrogenation of the CâC double bond gave the cisâannulated octahydrocyclopenta[c]pyridine (86â%), which was submitted to Fischer indolization (85â%). Although two regioisomers could be expected, only the angular constitution was observed. Relative and absolute configurations were established by Xâray crystallography of a paraâiodo benzamide derivative. The utility of the title compound as scaffold is further highlighted by a number of synthetically useful transformations, for instance formation of carboxamides, sulfonamides, ureas and reductive aminations with aldehydes
Octahydrocyclopenta[c]pyridine Scaffold â Enantioselective Synthesis and Indole Annulation
An optically active hexahydrocyclopenta[c]pyridine derivative with quaternary stereocenter was prepared as a new heterocyclic scaffold. Key reaction was the Pdâcatalyzed asymmetric allylic alkylation of a piperidineâbased ÎČâoxoester, which proceeded in very good yield with high level of enantioselectivity (90â%, 95â% ee). The αâallyl moiety was transformed into a 1,4âdiketone by Pdâcatalyzed Wacker oxidation with molecular oxygen (89â%). This intermediate was cyclized in an intramolecular aldol reaction furnishing the cyclopentenone motif (86â%). Hydrogenation of the CâC double bond gave the cisâannulated octahydrocyclopenta[c]pyridine (86â%), which was submitted to Fischer indolization (85â%). Although two regioisomers could be expected, only the angular constitution was observed. Relative and absolute configurations were established by Xâray crystallography of a paraâiodo benzamide derivative. The utility of the title compound as scaffold is further highlighted by a number of synthetically useful transformations, for instance formation of carboxamides, sulfonamides, ureas and reductive aminations with aldehydes
Palladium-Catalyzed Construction of Quaternary Stereocenters by Enantioselective Arylation of Îł-Lactams with Aryl Chlorides and Bromides
Herein, we report the first Pdâcatalyzed enantioselective arylation of αâsubstituted Îłâlactams. Two sets of conditions were developed for this transformation, allowing for the use of either aryl chlorides or bromides as electrophiles. Utilizing a highly electronârich, dialkylphosphine ligand, we have been able to construct αâquaternary centers in good yields (up to 91% yield) and high enantioselectivities (up to 97% ee)
Palladium-Catalyzed Construction of Quaternary Stereocenters by Enantioselective Arylation of Îł-Lactams with Aryl Chlorides and Bromides
Herein, we report the first Pdâcatalyzed enantioselective arylation of αâsubstituted Îłâlactams. Two sets of conditions were developed for this transformation, allowing for the use of either aryl chlorides or bromides as electrophiles. Utilizing a highly electronârich, dialkylphosphine ligand, we have been able to construct αâquaternary centers in good yields (up to 91% yield) and high enantioselectivities (up to 97% ee)
Formation of ÎŽâLactones by Cerium-Catalyzed, BaeyerâVilliger-Type Coupling of ÎČâOxoesters, Enol Acetates, and Dioxygen
Formation of ÎŽ-lactones is
observed when cyclopentanone-2-carboxylates
are converted in a cerium-catalyzed reaction with α-aryl vinyl
acetates under oxidative conditions. The products of this transformation
possess a 1,4-dicarbonyl constitution together with a quaternary carbon
center. Atmospheric oxygen is the oxidant in this process, which can
be regarded as ideal from economic and ecological points of view.
Further advantages of this new CâC coupling and oxidation reaction
are its operational simplicity and the application of nontoxic and
inexpensive CeCl<sub>3</sub>·7 H<sub>2</sub>O as precatalyst.
This so far unprecedented reaction is proposed to proceed via 1,2-dioxane
derivatives, which decompose under formation of an oxycarbenium cation
in a BaeyerâVilliger-type pathway. This mechanistic picture
is supported by the observation that electron-rich (donor substituted
or heteroaromatic) enol esters give higher yields than electron deficient
congeners. Apart from 1,4-diketones and α-hydroxylated ÎČ-oxoesters
formed as byproducts, the yields of ÎŽ-lactones range from moderate
to good (up to 74%)
Formation of ÎŽâLactones by Cerium-Catalyzed, BaeyerâVilliger-Type Coupling of ÎČâOxoesters, Enol Acetates, and Dioxygen
Formation of ÎŽ-lactones is
observed when cyclopentanone-2-carboxylates
are converted in a cerium-catalyzed reaction with α-aryl vinyl
acetates under oxidative conditions. The products of this transformation
possess a 1,4-dicarbonyl constitution together with a quaternary carbon
center. Atmospheric oxygen is the oxidant in this process, which can
be regarded as ideal from economic and ecological points of view.
Further advantages of this new CâC coupling and oxidation reaction
are its operational simplicity and the application of nontoxic and
inexpensive CeCl<sub>3</sub>·7 H<sub>2</sub>O as precatalyst.
This so far unprecedented reaction is proposed to proceed via 1,2-dioxane
derivatives, which decompose under formation of an oxycarbenium cation
in a BaeyerâVilliger-type pathway. This mechanistic picture
is supported by the observation that electron-rich (donor substituted
or heteroaromatic) enol esters give higher yields than electron deficient
congeners. Apart from 1,4-diketones and α-hydroxylated ÎČ-oxoesters
formed as byproducts, the yields of ÎŽ-lactones range from moderate
to good (up to 74%)
Three-Component Reaction toward Polyannulated Quinazolinones, Benzoxazinones, and Benzothiazinones
An efficient conversion of readily
accessible cyclic imines with
acid chlorides, that are able to take part in nucleophilic aromatic
substitution (S<sub>N</sub>Ar) reactions is realized in a new three-component,
one-pot reaction, giving at least tricyclic annulated quinazolinones,
benzoxazinones, and benzothiazinones as a result of the employed nitrogen,
oxygen, or sulfur nucleophiles, respectively. Especially in the case
of quinazolinones, this convenient strategy enables the access to
heterocycles of heightened diversity, which offer the development
of efficient derivatizations of the elaborated heterocyclic scaffolds.
In a subsequent Heck or Ullmann cyclization, further annulations to
the mentioned quinazolinones can be carried out
Three-Component Reaction toward Polyannulated Quinazolinones, Benzoxazinones, and Benzothiazinones
An efficient conversion of readily
accessible cyclic imines with
acid chlorides, that are able to take part in nucleophilic aromatic
substitution (S<sub>N</sub>Ar) reactions is realized in a new three-component,
one-pot reaction, giving at least tricyclic annulated quinazolinones,
benzoxazinones, and benzothiazinones as a result of the employed nitrogen,
oxygen, or sulfur nucleophiles, respectively. Especially in the case
of quinazolinones, this convenient strategy enables the access to
heterocycles of heightened diversity, which offer the development
of efficient derivatizations of the elaborated heterocyclic scaffolds.
In a subsequent Heck or Ullmann cyclization, further annulations to
the mentioned quinazolinones can be carried out
Coulomb excitation of 31Mg
The ground state properties of 31Mg indicate a change of nuclear shape at N = 19 with a deformed JÏ = 1/2+ intruder state as a ground state, implying that 31Mg is part of the âisland of inversionâ. The collective properties of excited states were the subject of a Coulomb excitation experiment at REXISOLDE, CERN, employing a radioactive 31Mg beam. De-excitation Îł -rays were detected by the MINIBALL
Îł -spectrometer in coincidence with scattered particles in a segmented Si-detector. The level scheme of 31Mg was extended. Spin and parity assignment of the 945 keV state yielded 5/2+ and its de-excitation is dominated by a strong collective M1 transition. Comparison of the transition probabilities of 30,31,32Mg establishes that for the N = 19 magnesium isotope not only the ground state but also excited states are largely dominated by a deformed pf intruder configuration.status: publishe
Electric quadrupole moments of the 2+_1 states in 100,102,104Cd
Using the REX-ISOLDE facility at CERN the Coulomb excitation cross sections for the 0+_gs â 2+_1 transition in the beta-unstable isotopes 100,102,104Cd have been measured for the first time. Two different targets were used, which allows for the first extraction of the static electric quadrupole moments Q(2+_1) in 102,104Cd. In addition to the B(E2) values in 102,104Cd, a first experimental limit for the B(E2) value in 100Cd is presented. The data was analyzed using the maximum likelihood method. The provided probability distributions impose a test for theoretical predictions of the static and dynamic moments. The data are interpreted within the shell-model using realistic matrix elements obtained from a G-matrix renormalized CD-Bonn interaction. In view of recent results for the light Sn isotopes the data are discussed in the context of a renormalization of the neutron effective charge. This study is the first to use the reorientation effect for post-accelerated short-lived radioactive isotopes to simultaneously determine the B(E2) and the Q(2+_1) values.status: publishe