Stereodivergent approach to both syn- and anti-isomers of γ-amino-β-hydroxy acids: (3S,4S)- and (3R,4S)-AHPPA derivatives

A stereodivergent approach employing an N-hydroxymethyl group has been utilized to produce both diastereomeric derivatives of (3S,4S)-AHPPA 3 and (3R,4S)-AHPPA 4, via an intramolecular conjugate addition and an intramolecular epoxidation, respectively. The selectivity of the intramolecular conjugate addition was more than 10:1 while that of the intramolecular epoxidation was more than 1:20.     

Naryl-substituted anthranilamides with intramolecular hydrogen bonds

Hydrogen bonding interaction as one type of non-covalent force has proven itself to be highly efficient for constructing structurally unique artificial secondary structures. Here, the structure of N_aryl-substituted anthranilamide in solution is demonstrated by various NMR technique, the intramolecular hydrogen bonds between amide attached to arylamine of the same ring is proposed, which is supported by its crystal structure in the solid phase. The substituent on the nitrogen atom of arylamine plays an important role in forming the presence of intramolecular hydrogen bonds. The chemical shift of the N_aryl-H downfield changes obviously, due to the formation of intramolecular hydrogen bonds and the deshielding effect of oxygen, and the neighboring C–H is activated and shows downfield protonic signal too. The presence of intramolecular hydrogen bonds probably provides the explanation for the transformation from N_aryl-substituted anthranilamide to imine, which could be converted into 2-aryl quinazolinone finally.     

Regioselective synthesis of C-prenylated flavonoids via intramolecular [1,3] or [1,5] shift reaction catalyzed by acidic clays

Prenyl side chain and dihydropyrano skeleton exists in many natural and synthetic biologically active flavonoids. A highly efficient and regioselective method for the synthesis of C-prenylated flavonoids via intramolecular [1,3] or [1,5] shift reaction of 5-O-prenylflavonoids catalyzed by Florisil or Montmorillonite clays is described. Florisil catalyzes intramolecular [1,5] shift reaction of 5-O-prenylflavonoids to obtain 8-C-prenylated flavonoids exclusively, Montmorillonite K10 exhibits the superior selectivity to promote intramolecular [1,3] shift reaction to obtain 6-C-prenylated flavonoids compared with Florisil and Montmorillonite KSF. This method provides a practical process to regioselective synthesize biologically important C-prenylated flavonoids in good yields using commercially available and inexpensive catalyst under mild conditions.     

A novel carbanion-olefin intramolecular cyclization: synthesis of substituted 2-aroyl-3,4-dihydro-2H-benzopyrans from salicylaldehydes

Utilization of a novel carbanion-olefin intramolecular 6-endo-trig cyclization reaction to provide 2-aroyl-3,4-dihydro-2H-benzopyrans is described. Through a sequence of a Wittig reaction, O-alkylation, and carbanion-olefin intramolecular cyclization, salicylaldehydes were converted into a series of new 2-aroyl-3,4-dihydro-2H-benzopyrans in two steps or in one-pot reaction.     

Sequential one-pot method for oxy-Michael addition,Heck coupling,and degradation followed by condensation: facile synthesis of 2-benzoxepin-3(1H)-ones

A sequential one-pot intermolecular oxy-Michael addition, intermolecular Heck coupling, and intramolecular degradation (retro-oxy-Michael addition) followed by condensation method has been developed for the synthesis of interesting 2-benzoxepin-3(1H)-ones. Significantly, the 2-benzoxepin-3(1H)-ones form the core quantum of biologically vital natural products. The initial oxy-Michael addition and Heck coupling steps involve a straight forward construction of C–O and C–C bonds, whereas, the final condensation step follows a novel mechanistic path via intramolecular degradation, double bond isomerization, and intramolecular condensation. Notably, a remarkable solvent effect has been observed in-order to promote the final intramolecular condensation.     

Efficient construction of novel α-keto spiro ketal and the total synthesis of (±)-terreinol

The first total synthesis of (±)-terreinol is described. An intramolecular Pd(II)-catalyzed cycloisomerization of a 2-(1′-alkynyl)benzyl alcohol via an apparent 6-endo diagonal pathway led to the 1H-isochromene ring system, which was further converted to the desired spiro ketal via an iodine-mediated intramolecular spiro-cyclization.     

Propargyl mediated intramolecular aglycon delivery (IAD): applications to the synthesis of core N-glycan oligosaccharides

The use of propargyl mediated intramolecular aglycon delivery (IAD) for the synthesis of the key Manβ(1→4)GlcNAc linkage of N-glycan oligosaccharides, including the core N-glycan pentasaccharide, is investigated. Isomerisation of a 2-O-progargyl group of manno thioglycoside donors to an allene is followed by iodonium ion mediated mixed acetal formation with the 4-OH of protected GlcNAc acceptors, and subsequent intramolecular glycosylation occurs with complete control of anomeric stereochemistry to form the Manβ(1→4)GlcNAc linkage. A variety of linear and convergent approaches (1+2, 3+1, 3+2) to the core pentasaccharide are investigated as means of probing the generality and limitations of this type of intramolecular aglycon delivery for the formation of β-mannoside linkages in complex oligosaccharides.     

Infrared study of intramolecular coordination in (chloromethyl)- and (dichloromethyl)-germanes

Frequencies (ν) and integrated intensities (A) of GeH stretching modes in the IR spectra of (diorgano)germanes containing GeCH₂Cl and GeCHCl₂ fragments have been measured. Anomalous values of ν and A (compared to those expected from the inductive effect only) are explained by intramolecular coordination between chlorine and germanium atoms. The enthalpy of intramolecular coordination (ΔH) has been determined by IR spectroscopy. The enthalpy of intramolecular coordination is shown to increase with the acceptor properties of the substituents bonded to the germanium atom in (dorgano)- and (triorgano)-germanes.     

Divergent reactivity of allene-containing α-diazoesters using Cu and Rh catalysis

A versatile intramolecular reaction of allene-containing diazomalonates that exhibits excellent chemoselectivity for either allenic C–H insertion or cyclopropanation is demonstrated. The identity of the product depends on the transition metal catalyst that is employed for the reaction. Rh catalysts promote exclusive C–H insertion with good diastereoselectivity for the trans product, while Cu catalysis enables intramolecular cyclopropanation to yield methylenecyclopropanes with moderate to good E:Z ratios.     

Synthetic studies on (−)-FR182877: construction of the ABCD ring system via the intramolecular cycloadditions (2)

Construction of the ABCD ring system of (−)-FR182877 via the intramolecular Diels-Alder (IMDA) reaction and the highly diastereoselective intramolecular hetero-Diels-Alder (IMHDA) reaction is described. The IMHDA reactions of the substrates incorporating the oxabutadiene with the E- or Z-alkene were examined, revealing that the sole product was obtained from both substrates and the E-alkene geometry was found to be crucial to obtaining the desired product.     

A novel intramolecular Ugi 3CC for the synthesis of N-alkyl-3-oxo-2-aryl-1,2,3,4-tetrahydropyrazino[1,2-a]indole-1-carboxamides

An intramolecular Ugi reaction of 2-(2-formyl-1H-indol-1-yl)acetic acid with aryl amines and isocyanides has been developed to produce a novel class of N-alkyl-3-oxo-2-aryl-1,2,3,4-tetrahydropyrazino[1,2-a]indole-1-carboxamides in good yields. This is the first report on intramolecular Ugi three component reaction of 2-(2-formyl-1H-indol-1-yl)acetic acid, aryl amine, and isonitrile.     

Dynamics of radiationless transitions in large molecules: 3. Decay of vibration-phonon states

The statistical operator of the ensemble of high-frequency intramolecular vibrations associated with the phonon reservoir depends on the phonon occupation numbers under thermal equilibrium conditions. The eigenvalues of energy of statistically averaged vibration-phonon (VP) states are complex quantities. In the case of weak VP coupling, only one- and two-phonon transitions are taken into consideration for calculating the decay rate constant, in which the difference of phonon energies compensates for the difference in energy between the initial and final intramolecular states. Although the fast evolution of amplitudes of VP states is due to intramolecular redistribution of energy and is not reduced to exponential decay of the initial state, the imaginary components of the eigenvalues coincide with those predicted by Fermi’s golden rule. The relative contribution of two-phonon (combination) transitions compared with one-phonon transitions increases with an increase in the density of intramolecular states and temperature, becoming prevalent for large molecules at T ≥ D ? Δ₀ (D = 100–200 K (70–140 cm^?1) is the Debye temperature and Δ₀～10 cm^?1 is the spacing between neighboring intramolecular vibration levels). When T ≥ D, the decay rate constant is K ∝ T ².     

β-Mannosylation of N-acetyl glucosamine by propargyl mediated intramolecular aglycon delivery (IAD): synthesis of the N-glycan core pentasaccharide

An efficient and completely stereocontrolled synthesis of the N-glycan Manβ(1-4)GlcNAc disaccharide is achieved by propargyl mediated intramolecular aglycon delivery (IAD). Isomerisation of the 2-O-progargyl group of a manno thioglycoside to an allene is followed by iodonium ion mediated mixed acetal formation with the 4-OH of a protected GlcNAc derivative, and subsequent intramolecular glycosylation with complete control of anomeric stereochemistry. Access to this key disaccharide intermediate allows completion of the total synthesis of the core N-glycan pentasaccharide.     

Intramolecular excimer formation in macromolecules—V. Head-to-head polystyrene,block copolymers of styrene and butadiene and regular condensation polymers of α-methylstyrene

Studies of the photophysical properties of head-to-head polystyrene, block copolymers poly(butadiene-b-styrene) and polystyrenes of various sequence length of styrene chromophore and regular copolymers of α-methylstyrene indicate that interactions between phenyl chromophores located distantly upon the macromolecule are not of major significance in determination of excimer formation in styrene polymers. It is concluded that intramolecular excimer formation in polystyrenes occurs primarily as a consequence of interactions between nearest neighbour chromophores in the polymer chain. The influence of polymer coil dimensions upon intramolecular excimer formation is demonstrated. The photophysical behaviour of poly(butadiene-b-styrene) block copolymers shows the importance of intramolecular energy migration in population of potential excimer sites.     

Pd(II)-catalyzed cascade Heck/intramolecular C(sp2)–H amidation reaction: An efficient route to 4-aryl-2-quinolinones

A Pd(II)-catalyzed cascade Heck/intramolecular C(sp²)–H amidation reaction is described for the synthesis of 4-aryl-2-quinolinone derivatives. Substituted cinnamamide containing 2-(pyridin-2-yl)ethanamine unit reacts with aryl iodide to form intermediate by Heck reaction. Then, the intermediate takes place intramolecular amidation via C(sp²)–H activated process promoted by orientation group.     

Synthesis of the 11-membered ring of the marine alkaloids, madangamines

The first successful attempt at synthesizing the 11-membered ring of madangamine alkaloids is described. The synthesis involves intramolecular N,O-acetalization of a cyclohexanone derivative, cross-coupling reaction with (Z)-vinylstannane, and intramolecular reductive amination for elaboration of the 11-membered macrocycle.     

Photophysics of intramolecular electron donor—acceptor systems; N-carbazolyl(CH2)ntetrachlorophthalimide

In systems N-carbazolyl—(CH₂)_n—tetrachlorophthalimide (n = 2, 3, 4, 7) virtually complete quenching of the carbazole fluorescence via an intramolecular electron-transfer mechanism occurs, with concomitant formation of an emissive polar excited state. The rate of formation of this polar excited state is found to exceed considerably those reported for formation of intramolecular exciplex states in other non-conjugated bichromophoric systems with a less pronounced electron donor—acceptor character.     

FT-IR and FT-Raman study of hydrogen bonding in p-alkylcalix[8]arenes

The FTIR and FT Raman spectra of p-alkylcalix[8]arenes (alkyl = tert-butyl, isononyl) were recorded. Analysis of IR spectra showed that the cyclic cooperative intramolecular hydrogen bond is realized in calix[8]arene. It was found that the strength of the cyclic cooperative intramolecular hydrogen bond in the series of alkyl derivatives of calix[8]arenes depends very little on the replacement of the p-tert-butyl groups by the more bulky isononyl group. From our data follows that the orientation of aromatic fragments in calixarene molecules depends on the type of alkyl substituent.An analysis of the changes in the IR spectra with heating and dissolution shows that the conformation of the “pleated-loop” is retained in p-tert-butylcalix[8]arene. It turned out that the intramolecular hydrogen bond is a “probe” of the conformation of calixarene molecules and IR spectroscopy is a unique method that allows one to follow the slightest nuances of changes in the H-bound system of these supermolecules.     

Examination of the mechanism of the intramolecular amination of N-(3-bromopyridin-2-yl)azaheteroarylamines and N-(2-chloropyridin-3-yl)azaheteroarylamines: a Pd-catalyzed amination and/or a base-assisted nucleophilic aromatic substitution?

The intramolecular amination of N-(3-bromopyridin-2-yl)azaheteroarylamines and N-(2-chloropyridin-3-yl)azaheteroarylamines was investigated. In this way we unraveled the mechanism of the ring closure reaction in the auto-tandem amination (inter- and intramolecular Pd-catalyzed amination) of 2,3-dibromopyridine with amino(benzo)(di)azines and 2-chloro-3-iodopyridine with amino(benzo)(di)azines, respectively. Depending on the substrate a Pd-catalyzed amination, a base-assisted nucleophilic aromatic substitution or a combination of both is occurring. An explanation based on the aromaticity of the amidine, supported by theoretical calculations, is provided. In addition we gained evidence that the intramolecular metal-catalyzed amination of N-(3-bromopyridin-2-yl)azaheteroarylamines and N-(2-chloropyridin-3-yl)azaheteroarylamines indeed involves a nitrogen atom that is not substituted with a hydrogen atom.