End-capping of a pseudorotaxane via Diels-Alder reaction for the construction of C60-terminated [2]rotaxanes

[reaction: see text] The Diels-Alder reaction of various dienophiles such as C(60) with a pseudorotaxane having a sultine moiety afforded corresponding [2]rotaxanes in moderate yields. The introduction of a porphyrin moiety on the wheel component considerably enhanced the efficiency of the end-capping reaction with C(60).     

Synthesis of alicyclic esters via an intramolecular conjugate addition reaction. New method for generating (Z)-vinylcopper species from 1,1-dibromoalkenes

A novel cyclization reaction of a 1,1-dibromoalkene derivative having an α,β-unsaturated ester moiety was developed. Under the influence of Me₂CuLi, the 1,1-dibromoalkene was converted into a (Z)-vinylcopper species which in turn underwent an intramolecular conjugate addition reaction with the α,β-unsaturated ester moiety. Five-, six-, and seven-membered carbocycles were constructed by the present method. The substrate having an epoxide moiety also afforded a five-membered product via a 5-exo type intramolecular cyclization reaction.     

Solvent-dependent changes in the ene reaction of RTAD with alkenes: the cyclopropyl group as a mechanistic probe

[reaction: see text] The vinylcyclopropyl moiety was used as an efficient probe to test mechanistic possibilities of the triazolinedione-alkene ene reaction. In non-hydroxylic solvents, this reaction afforded only the ene adducts via a closed three-membered aziridinium imide (AI) intermediate, whereas in hydroxylic solvents a dipolar intermediate is favored and trapped by the cyclopropyl moiety to form the corresponding cyclopropyl-rearranged solvent-trapped adducts.     

Asymmetric induction of the iodolactonization reaction of alpha-sulfurated gamma-unsaturated amides

The 1,3-asymmetric iodolactonization reaction of enantiopure alpha-sulfurated gamma-unsaturated amides has been investigated. With sulfinyl and sulfonyl groups, a poorly stereoselective reaction was observed, whereas with a sulfanyl moiety, the diastereoselectivity can be high as 96:4. The role of the oxygen atom on the sulfur moiety is discussed.     

Competitive thermal ene reaction and Diels-Alder reactions of 2-[N-(alk-2-enyl)benzylamino]-3-vinylpyrido[1,2-a]pyrimidin-4(4H)-ones

Thermal reaction of 2-[N-(alk-2-enyl)benzylamino]-3-(2-substituted and 2,2-disubstituted)vinylpyrido[1,2-a]pyrimidin-4(4H)-ones gave azepine, the desired ene products, and/or pyran derivatives. The formation of the latter was responsible for the [4+2] cycloaddition reaction between the α,β-unsaturated ester carbonyl moiety as a diene part and the alkenylamino moiety as an ene one. The reaction features depended upon the kinds of substituents both on the vinyl and alkenyl counterparts; strongly electron-withdrawing substituents on the vinyl moiety or an electron-donating substituent on the alkenyl one changed the reaction feature from the ene reaction to the hetero Diels-Alder reaction.     

Regio- and stereoselective transfer of p-toluenesulfonamido group from sulfur to carbon: preparation of aminoalcohol derivatives from allylalcohols

A novel methodology for the regio- and stereoselective synthesis of amino alcohol derivatives from allylalcohols/ethers via intramolecular nucleophilic participation by the sulfilimine moiety is disclosed. The sulfilimine moiety is stereospecifically transformed to a sulfinyl moiety with an inverted configuration. The reaction is general and affords highly functionalised products.     

Axially chiral dicarboxylic acid-catalyzed asymmetric imino aza-enamine reaction/oxidation as a Strecker reaction surrogate

Axially chiral dicarboxylic acid-catalyzed highly enantioselective imino aza-enamine reaction was elaborated into a surrogate of the asymmetric Strecker reaction building on the fact that the N,N-dialkylhydrazone moiety can be easily converted to the cyanide moiety by treatment with peracid.     

An efficient three-component synthesis of new barbiturate salts

An efficient synthesis of new barbiturate salts consist of 2-aminopyridinium moiety by a?n uncatalyzed three-component condensation reaction of C–H acids, pyrimidine-tetraones, and 2-aminopyridines? in refluxing chloroform is reported. The reaction of pyrimidine-tetraones and 2-aminopyridines with ninhydrin in the formation of new barbiturate salts consist of 2-aminopyridinium moiety is also investigated.     

Dehydrogenative Diels-Alder reaction

The dehydrogenative cycloaddition of dieneynes, which possess a diene in the form of a styrene moiety and a dienophile in the form of an alkyne moiety, produces naphthalene derivatives when heated. It was found that a key requirement of this process is the presence of a silyl group attached to the alkyne moiety, which forces a dehydrogenation reaction to occur.     

Energy transfer switching in a bistable molecular machine

[reaction: see text] A novel [2]rotaxane, containing pyrene and perylene bisimide as both stoppers and photoactive units, has been prepared. The shuttling of the protonated macrocycle switched the energy transfer (EN) from a pyrene moiety to a perylene moiety, which resulted in changes of fluorescence of the perylene moiety.     

Cyclic boronates in the mass spectrometry of ecdysteroids

For the structural elucidation of ecdysteroids a reaction with phenylboronic acid has been employed. This reaction takes place exclusively on the C20,C22 diol moiety, thus facilitating fast and easy detection of this moiety in the molecule od ecdysteroid. This derivatization also redirects fragmentation to C17/C20 bond cleavage with charge retention on both fragments enabling assessment of the structure both of the steroid nucleus and of the side-chain. Possible reaction of phenylboronic acid with the diol moiety of the glycosyl group of the glycoside od ecdysteroid, producing di-adduct, is demonstrated; participation of the 5β-hydroxy group of 5β,20-dihydroxyecdysone in the formation of such a di-adduct is discussed; and the role of theenol form of the 6-carbonyl group is proved.     

Diastereoselective Total Synthesis of (±)‐Schindilactone A,Part 1: Construction of the ABC and FGH Ring Systems and Initial Attempts to Construct the CDEF Ring System

First‐generation synthetic strategies for the diastereoselective total synthesis of schindilactone A ( 1 ) are presented and methods for the synthesis of the ABC, FGH, and CDEF moieties are explored. We have established a method for the synthesis of the ABC moiety, which included both a Diels–Alder reaction and a ring‐closing metathesis as the key steps. We have also developed a method for the synthesis of the FGH moiety, which involved the use of a Pauson–Khand reaction and a carbonylative annulation reaction as the key steps. Furthermore, we have achieved the construction of the central 7–8 bicyclic ring system by using a [3,3]‐rearrangement as the key step. However, unfortunately, when this rearrangement reaction was applied to the construction of the more advanced CDEF moiety, the anticipated annulation reaction did not occur and the development of an alternative synthetic strategy would be required for the construction of this central core.     

Thermal chemistry of poly(aryl ether phthalazine)s and the synthesis of poly(aryl ether quinazoline)s

Poly(aryl ether phthalazine)s were found to undergo an exothermic reaction at a temperature range of 360–440°C. We elucidated the origin of the exothermic reaction and the physiochemical phenomena associated with it, based on thermal analyses, model compound studies, and ¹³C solid-state NMR studies. At elevated temperatures, polymers containing a diphenylphthalazine moiety 4 underwent extensive thermal crosslinking reactions as a result of a nitrogen elimination reaction of the phthalazine moiety. However, polymers containing the tetraphenyl or hexaphenyl phthalazine moiety 5 and 6 were found to undergo principally a backbone rearrangement reaction, in which the phthalazine moiety rearranged to a quinazoline. Utilizing this efficient thermal rearrangement of polyphenylated phthalazines, we have prepared a novel activated difluoride, 2,4-bis(4-fluorophenyl)-,5,6,7,8-tetraphenylquinazoline 9d, which underwent high-temperature solution polycondensation with BPA to give the quinazoline containing poly(aryl ether) 14. Polymer 14 is amorphous, has a glass transition temperature of 264°C, and has high thermooxidative stability with 5% weight loss being recorded at 514°C in nitrogen. © 1996 John Wiley & Sons, Inc.     

A general and efficient five-step one-pot procedure leading to nitrogen-bridgehead heterocycles containing an imidazole ring

A very simple annulation reaction was designed, allowing an imidazole moiety to be fused onto a range of pyridine-based derivatives. The methodology consists of an activation step via the formation of a pyridinium salt to increase the electrophilicity of the pyridine ring, followed by a cascade reaction triggered by a nucleophilic attack of the iminium moiety. Depending on the pyridinium salt, it is possible to obtain functionalized imidazole moieties.     

Synthesis of reactive poly(norbornene): Ring‐opening metathesis polymerization of norbornene monomer bearing cyclic dithiocarbonate moiety

A norbornene monomer bearing cyclic dithiocarbonate moiety (NB‐DTC) was successfully synthesized from the corresponding precursor having epoxy moiety by its reaction with carbon disulfide. NB‐DTC underwent the ring‐opening metathesis polymerization (ROMP) catalyzed by a ruthenium carbene complex to give the corresponding poly(norbornene). The dithiocarbonate moiety incorporated into the side chain of the obtained poly(norbornene) reacted with amine to afford the corresponding thiourethane moiety with thiol group, which underwent oxidative S‐S coupling and/or addition reaction to the C‐C double bond in the main chain, leading to formation of a cross‐linked polymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Synthetic utility of glycosyl triazoles in carbohydrate chemistry

We report herein a study of the synthetic utility of the glucosyl triazole moiety in carbohydrate chemistry. A model glucosyl triazole was prepared by a modified Huisgen 1,3-dipolar cycloaddition reaction. The relative rate of cycloaddition was investigated using a variety of alcohol co-solvents and reaction temperatures. It was found that the reaction proceeded with similar efficiency irrespective of co-solvent, however mildly elevated temperatures (40 °C cf. rt) increased the speed of reaction significantly (2 h cf. 8 h). The robustness of the triazole moiety was then interrogated under conditions typically encountered in carbohydrate chemistry reaction sequences—alcohol group protection/deprotection, nucleophilic displacement, and O-glycosylation. The triazole integrity was retained in all cases studied as evidenced from full compound characterization. Finally, a diverse set of triazole-linked glycoconjugates was synthesized. Collectively, our results demonstrated that the glucosyl triazole moiety was indeed a robust entity for carbohydrate chemistry.     

ON THE SPATIAL CORRELATION BETWEEN THE PROTEIN SURFACE AND THE ELECTRON TRANSFER CYCLE IN BACTERIAL PHOTOSYNTHETIC REACTION CENTERS

Abstract— n -Doxylstearic acids are shown to be electron acceptors in reaction centers from R. spheroides R-26 mutant illuminated with 860 nm light. The electron accepting efficiency varies with n , thus with the location of the nitroxide moiety on the stearic acid chain, and is maximum for 12-doxylstearic acid. In this molecule the nitroxide moiety is 1.4 nm from the polar carboxyl carbon based on molecular models. If the nitroxide moiety is located in or near the polar reaction center protein surface, the results suggest that the quinone-iron complex, which is the ultimate electron acceptor from a bacterio-chlorophyll dimer in the reaction center, is located ∼ 1.4 nm from the protein surface. The protein itself is estimated to have a diameter of 5.4 nm assuming spherical symmetry, so it is postulated that the quinone-iron complex is located on one side of the protein.     

Iron‐Catalyzed Radical Cleavage/C−C Bond Formation of Acetal‐Derived Alkylsilyl Peroxides

A novel radical‐based approach for the iron‐catalyzed selective cleavage of acetal‐derived alkylsilyl peroxides, followed by the formation of a carbon–carbon bond is reported. The reaction proceeds under mild reaction conditions and exhibits a broad substrate scope with respect to the acetal moiety and the carbon electrophile. Mechanistic studies suggest that the present reaction proceeds through a free‐radical process involving carbon radicals generated by the homolytic cleavage of a carbon–carbon bond within the acetal moiety. A synthetic application of this method to sugar‐derived alkylsilyl peroxides is also described.     

Synthesis and characterization of bioorganometallic conjugates composed of NCN-pincer platinum(II) complexes and uracil derivatives

The conjugation of the NCN-pincer platinum(II) complexes as an oraganometallic compound and the uracil derivatives as a nucleobase was demonstrated to give the corresponding bioorganometallics. The NCN-pincer ligands bearing the 6-ethynyl-1-octyluracil, 5-ethynyl-1-octyluracil, and the furanopyrimidine moiety were synthesized. In a crystal state, the NCN-pincer ligand bearing the 6-ethynyl-1-octyluracil moiety was found to form a hydrogen-bonded dimer through intermolecular hydrogen bonds between the uracil moieties, which was connected through π-π interaction between the uracil and benzene moieties of the NCN-pincer ligand. The reaction of the NCN-pincer ligand bearing the 6-ethynyl-1-octyluracil moiety with [Pt(tolyl-4)₂(SEt₂)]₂ led to the formation of the NCN-pincer platinum(II) complex bearing the 6-ethynyl-1-octyluracil moiety. The NCN-pincer platinum(II) complex bearing the furanopyrimidine moiety was obtained by the reaction of the NCN-pincer ligand bearing the furanopyrimidine moiety with [Pt(tolyl-4)₂(SEt₂)]₂. The single-crystal X-ray structure determination of the NCN-pincer platinum(II) complex bearing the furanopyrimidine moiety revealed the formation of the furanopyrimidine ring and the π stack dimer between the furanopyrimidine and benzene moieties of the NCN-pincer ligand in the crystal packing. The NCN-pincer platinum(II) complexes bearing the 6-ethynyl-1-octyluracil moiety or the furanopyrimidine moiety exhibited emission in both solution and solid states.     

Synthesis of (+/-)-madindolines and chemical models. Studies of chemical reactivity

[reaction: see text] The madindolines are believed to inhibit cytokine signaling through the gp130 receptor. Model compounds of madindolines were synthesized and tested for thiol reactivity. The heterocyclic moiety of madindoline was shown to form thiol adducts via the Savige-Fontana reaction. The enedione moiety was found to be unreactive toward simple thiols unless the quaternary center was removed. Using the powerful Moore reaction, we have synthesized (+/-)-madindoline A and B in 11 steps.