Regioselectivity of the insertion reactions of some aromatic diazo compound complexes with cyclomaltoheptaose

Trifluoromethylphenylcarbenes. Carbene-Carbene Interconversion on the Singlet Energy Surface and Rearrangement to Trifluorobenzocyclobutene, Trifluorostyrene, and Trifluoromethylfulvenallenes

The four isomeric α-, ortho-, meta-, and para-trifluoromethylphenylcarbenes were generated by photolysis of the corresponding 3-phenyl-3-trifluoromethyldiazirene 1 or the four isomeric trifluoromethylphenyldiazomethanes 2 and 4–6. The four corresponding triplet trifluoromethylphenylcarbenes 3 and 7–9 were observed by electron spin resonance (ESR) spectroscopy in Ar matrices at 14 K. The α- and ortho-carbenes 3 and 7 and the ortho- and para-carbenes 7 and 9 interconvert partially when generated by short-wavelength photolysis (350 nm) before intersystem crossing to the triplet states. The triplet states do not undergo further Carbene-Carbene interconversion. The interconversions are assumed to take place via the meta-trifluoromethylphenylcarbene 8. When the ortho- and para-carbenes are generated by long-wavelength photolysis (>450 nm), the discrete, non-interconverting triplet carbenes are observed in the ESR spectra. Flash vacuum thermolysis of the diazirene 1 at 500°C afforded a mixture of bis(trifluoromethyl)heptafulvalenes 11, bis(trifluoromethyl)stilbenes 12, and bis(trifluoromethyl)anthracenes 13, and the presence of their likely precursor(s), trifluoromethylcycloheptatetraene(s), was confirmed by a peak at 1830 cm–1 in the Ar matrix IR spectrum. In addition, at 700°C, four monomeric carbene rearrangement products were isolated and characterised, viz. 1,1,2-trifluorobenzocyclobutene 14, 1′,2′,2′-trifluorostyrene 15, and 1- and 2-trifluoromethylfulvenallenes 16 and 17.

Improved access to 2-O-monobenzyl ethers of β-cyclodextrin as precursors of catalysts for organophosphoryl esters hydrolysis

A comparative study of reaction conditions was performed for the synthesis of a 2-O-monobenzyl ether of cyclomaltoheptaose (beta-CD). Optimal conditions involved sodium ethoxide in Me(2)SO and benzyl bromide. The methodology was extended to the preparation of various 2(I)-O-iodobenzyl and 2(I)-O-carboxymethylbenzyl derivatives of beta-CD including a 3-carboxymethyl-4-iodobenzyl derivative of interest as precursor of an enzyme mimic to degrade the organophosphoryl ester diethyl 4-nitrophenyl phosphate (paraoxon).

Applications of modified cyclodextrins

One of the key areas of importance in biotechnology and bioengineering is molecular complexation (MC). MC is useful in selectivity, separation, and solubilization of biomolecules. While many complex, natural MC agents exist, such as proteins and antibodies, relatively few engineered MC materials are available. Inorganic, insoluble MC agents, such as zeolites, are widely used in petroleum catalysis. Carbon Buckminster fullerenes ("bucky balls") can complex small neutral molecules, but are relatively insoluble and difficult to manufacture. Crown ethers have been used for molecular complexation, but are costly to synthesize and have limited capacities. One class of highly useful MC agents are cyclodextrins (CDs). These naturally-occurring, water-soluble cyclic glucans are used in a variety of food, pharmaceutical, and analytical applications. Due to the availability of multiple reactive hydroxyl groups, the functionality of CDs can be greatly increased through chemical modification. A host of new applications are being explored, including enzyme mimicry, molecular recognition, chromatographic separation, and solubilization. This review describes recent applications of modified cyclodextrins in bioprocessing and medicine.

Inter- and innermolecular reactions of chloro(phenyl)carbene

Supramolecular photolyses of 3-chloro-3-phenyl-3H-diazirine (8) were performed within cyclodextrin (CyD) hosts to determine whether these toroidal inclusion compounds could alter the reactivity of the ensuing carbene reaction intermediate, chloro(phenyl)carbene (9). Remarkably, no intramolecular products stemming from carbene 9 could be detected. Instead, modified CyDs were formed via so-called innermolecular reactions. Hence, diazirine 8 was photolyzed in various conventional solvents to gauge the intermolecular reactivity of carbene 9. Relevant results were used to rationalize the CyD innermolecular reaction products.

Chemospecific monofunctionalization of alpha-cyclodextrin in the solid state

[reaction: see text] The properties of the self-assembling aziadamantane inclusion complex with two alpha-cyclodextrin molecules have been exploited to perform a chemospecific monofunctionalization of alpha-cyclodextrin. The insertion of the photochemically generated carbenes takes place chemospecifically into the cyclodextrin's C-3-OH and C-2-OH bonds in 39 and 18% yield, respectively. This model reaction surpasses conventional methods in terms of yield as well as selectivity.

Regioselective synthesis and characterization of naphthylethylcarbamoyl-beta-cyclodextrins

Regioselective reactions of 1-(1-naphthyl)ethyl isocyanate (NEIC) with beta-cyclodextrin (beta-CD) were studied with and without NaH activation of beta-CD in N,N-dimethylformamide (DMF) and pyridine. All six possible monosubstituted CD products were separated and characterized by proton NMR. Primary substitution product predominates when the reaction was carried out under reflux condition in pyridine without NaH activation. The C-2 substitution product predominates when the reaction was carried out in DMF. Conversion of 2-O-(1-(1-naphthyl)ethylcarbamoyl)-beta-CD to 6-O-(1-(1-naphthyl)ethylcarbamoyl)-beta-CD was observed when NaH was used to activate hydroxyl groups of CD.