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The mechanistic pathway for the formation of 1,2-oxazetes by reaction of olefins with nitrous anhydride has been clarified. The initial reaction intermediate, a β-nitroso nitrite ester that is sensitive to light, undergoes O-NO fission to form a β-nitroso alkoxy radical, even with ambient fluorescent lighting but much faster with blue light irradiation. The oxygen of the alkoxy radical subsequently adds to the adjacent nitroso group to generate a cyclic four-membered nitrosyl radical. The 1,2-oxazete is then produced by elimination to generate the C═N bond. No 1,2-oxazete formation occurs in the dark.

Triflyl nitrate is easily generated from tetra-n-butylammonium nitrate in CH2Cl2 solution and serves as an effective nitrating agent for a wide range of unsaturated substrates to form nitro olefins.

Concise stereocontrolled synthetic routes to the C2-symmetric azatetraquinane 1 (or, also, the enantiomer) are described. The successful execution of the synthesis involved innovation in the method...

Nitrosyl triflate (TfONO) can be generated

A study of [3 + 2] cycloaddition reactions of a bicyclic nitrone with various cyclopentenes has clarified the diastereomeric preferences as a function of the olefinic structure. It has also identified an important stereochemical difference between nitrones and the analogous azomethine ylides in [3 + 2] cycloaddition reactions.

An efficient CuBr2-catalyzed diastereoselective allylation of a cyclic hemiacetal with allyltrimethylsilane as a nucleophile has been developed. The protocol offers a cost effective, protecting group tolerant, and operationally simple approach to 2,6-trans-disubstituted tetrahydropyran with excellent diastereoselectivity. Furthermore, the application of this methodology has been demonstrated in the total synthesis of decytospolides A and B and their C6-epimers.

Concise stereocontrolled synthetic routes to the C

The first asymmetric total synthesis and stereochemical assignments of 10-membered macrolactones relgro and 10'-oxorelgro are disclosed. To this end, palladium-catalyzed Stille coupling, the Mitsunobu reaction, ring-closing metathesis, EDCI promoted coupling and the Jacobsen hydrolytic kinetic resolution are used as key steps. The total synthesis followed by thorough evaluation of the optical rotation and CD spectral data led to the revision of the absolute configuration at C-6' for both relgro and 10'-oxorelgro. Moreover, the 1H as well as 13C NMR data are reported for the first time for relgro.

An efficient CuBr

A highly regioselective gold(I)-catalyzed 6-endo-dig cyclization of 2,2-dimethyl-5-(alkynyl)-4H-benzo[d][1,3]dioxin-4-ones for the synthesis of 8-hydroxy-3-substituted isocoumarins is described. Key features of the reaction include the broad substrate scope, scalability, and tolerance for protecting groups. The synthetic utility of this novel method is demonstrated by the first total synthesis of exserolide F, an isocoumarin-containing polyol natural product.

The first asymmetric total synthesis of a 16-membered macrolide, aspergillide D, is described. The chiral centers of the acid are derived from d-ribose and the alcohol subunit from 1,8-octane diol through Sharpless kinetic resolution, respectively. The other key reactions include Yamaguchi esterification, ring-closing metathesis reaction, and Shiina macrolactonization to construct the fully functionalized macrocycle.

A highly stereoselective synthesis of the C-8–C-24 fragment of maltepolide C has been achieved in a convergent and efficient manner by utilizing a tandem Sharpless asymmetric dihydroxylation (SAD)/SN2 cyclization reaction sequence as the key step. Other important steps include a Crimmins-modified Evans aldol reaction, a Brown asymmetric allylation, a Horner–Wadsworth–Emmons olefination, and a Corey–Bakshi–Shibata (CBS) reduction.

The first asymmetric convergent total synthesis of four isomers of proposed structures of cryptorigidifoliol K (1a, 1b, 1c, and 1d) has been achieved from commercially available starting materials. The key steps in this synthesis involve tandem isomerization followed by a C–O and C–C bond-forming reaction for the construction of trans-2,6-disubstituted dihydropyran, iodolactonization, isomerization of terminal alkene, and cross-metathesis reaction. The large discrepancies in the spectroscopic data (1H NMR) of synthetic cryptorigidifoliol K from the natural product suggest that the structure of the natural cryptorigidifoliol K requires revision.

A unified and efficient synthetic route for both tetraketide (1) and cryptorigidifoliol I (2) has been devised successfully from commercially available starting materials in 11 and 17 steps, with 16% and 11% overall yields, respectively. Highlights of the syntheses involved sequential Lewis acid-catalyzed highly regio- and diastereoselective allylations and intramolecular Mitsunobu lactonization.

Novel sulfone-linked bis heterocycles pyrazolines in combination with thiadiazoles, oxadiazoles and triazoles were prepared from E-styrylsulfonylacetic acid methyl ester and tested for their antimicrobial activity. The compound 8 showed pronounced activity than the compounds 6 and 7.

α-Arylidene-γ-phenyl-Δβ,γ-butenolides were converted to the respective γ-butyrolactones in methyl alcohol with sodium borohydride in presence of triethylamine in a single pot. *IICT communication No. 4391.

Treatment of tetrahydropyranyl ethers with cerium (III) chloride heptahydrate in methanol provides a simple, convenient and selective method for detetrahydropyranylation, and the parent alcohols are obtained in high yields.

Treatment of aryl and alkyl tosylates with Cerium(III) chloride hepta hydrate and sodium iodide in acetonitrile provides a simple, convenient and chemoselective procedure for the de tosylation.

A mild, novel and chemoselective method for the deprotection of allyl ethers by a CeCl 3 .7H 2 O NaI system is described.

1,1-Diacetates are efficiently deprotected by using CeCl 3 . 7H 2 O-Nal system affording the aldehydes in high yields.

α-Arylidene-γ-phenyl-Δβ,γ-butenolides were converted to the respective γ-butyrolactones in methyl alcohol with sodium borohydride in presence of triethylamine in a single pot. *IICT communication No. 4391.

A new class of 1,3,4-oxadiazoles were prepared from acid hydrazides on treatment with different carboxylic acids in the presence of phosphorus oxychloride. Interconversion of oxadiazoles to thiadiazoles and triazoles was carried out with appropriate reagents. The antimicrobial and cytotoxic activities of compounds 7a-d to 12a-d were tested. Compounds 10d and 12d showed pronounced antimicrobial activity. Further, compound 10d exhibited maximum cytotoxicity. (C) 2008 Elsevier Masson SAS. All rights reserved.

Treatment of tetrahydropyranyl ethers with cerium (III) chloride heptahydrate in methanol provides a simple, convenient and selective method for detetrahydropyranylation, and the parent alcohols are obtained in high yields.

A mild, novel and chemoselective method for the deprotection of allyl ethers by a CeCl 3 .7H 2 O NaI system is described.

The electron impact (EI) and chemical ionization (CI) spectra of 2,2-diphenyl-3-aryl cyclobutanone oximes (1–5) are reported. Formation of diphenylmethyl cation at m/z 167 is a major fragmentation process in both EI and CI spectra. Labelling studies established that the hydrogen involved in this rearrangement transfers from the NOH group and not from cyclobutane ring positions. The [M + 3]+ ions are formed under CI conditions as a result of CN double bond reduction. An interesting secondary kinetic isotope effect is observed in the formation of ion e at m/z 183 in both EI and CI spectra. Other characteristic fragmentation pathways occurring in the EI and CI spectra of these compounds are outlined.

In contrast to the usual expectation in chemical ionization (CI) mass spectrometry, the CI spectra of a series of aryl 4-nitro-Δ'-cyclohexenes show very low intensity protonated molecular ions while a major share of the ion current is carried by rearrangement ions. The intervention of a rearrangement long known in the solvolysis of cyclohexenyl carbenium ions can account for the observed CI behaviour.

The effect of change on the racemisation of Lalanine in Co(III) complexes has shown that racemisation rates are directly proportional to the charge on the complex from a − through zero to a +2 charge. Although Co(III) complexation increases the rates of racemisation of amino acids, complexation of dipeptides to Co(III) reduces the rates of racemisation. The larger the positive charge on the complex, however, the faster is the rate racemisation.

The study examined the effect of Ni(II), Zn(II), Cu(II), Co(II) and Pd(II) ions on the rate of racemisation of L -serine and L -threonine. All ions except Ni(II) enhanced the racemisation of serine; the retarding effect of Ni(II) increased with ion concentration. Both Zn(II) and Ni(II) ions retarded the racemisation of threonine.

Curie-point pyrolysis products obtained from Val-Pro, Pro-Val, Ala-Pro, Pro-Ala, Gly-Ala, and Ala-Gly and their diketopiperazines (DKPs) were analysed by gas chromatography–mass spectrometry. The dipeptides readily formed corresponding DKPs by losing water molecules. The DKP in turn produced two to six primary products with an expulsion of simple molecules such as H2, propene, and CO. The products formed in low or trace amounts constitute secondary products. Bimolecular condensation to form products (17), (19), (23), (27), and (30) was also seen. The results showed that this can be a rapid method for characterising the structural features of these residues in complex systems.

Evidence for the gas phase equilibration of triphenyl cyclohexenyl and diphenyl cyclopentenyl benzyl cations directly or through common intermediates has been obtained from chemical ionization/collisional activation and kinetic energy release data.

Stereochemical effects were observed in the electron ionization, methane, isobutane and ammonia positive ion chemical ionization and hydroxy negative ion chemical ionization behaviour of some isomeric triaryl nitrocyclohexenes. cis-Eliminations leading to loss of HNO2, H2NO2 and arene were found to be stereochemically preferred in gaseous ions.

Comparaison entre [Ni(gly) 2 ]•2H 2 O, [Co(gly) 3 ]•2H 2 O et [Cu(gly) 2 ]•H 2 O dans la reaction avec C 6 H 5 -H 2 -Cl, (p)Cl-C 6 H 4 -CH 2 -Cl et (p)CH 3 -C 6 H 3 -CH 2 -Cl