Intramolecular electrophilic displacement of acyl by nitro group during attempted synthesis of 3-nitrocoumarins

2-Hydroxyacetophenones undergo upon nitration in acetic acid a substitution of the acyl by nitro group followed by an intramolecular 1,3-acyl shift reminescent of a retro-Fries rearrangement to yield phenyl esters.     

Exploration of the biomimetic synthesis of indole-diterpene mycotoxins: an unexpected cascade reaction during the attempted synthesis of emindole SB

The key step in an attempted biomimetic synthesis of the indole-diterpene mycotoxin emindole SB delivers the pentacyclic compound resulting from 6-endo cyclisation instead of the product arising by the 5-exo reaction required in the putative biosynthetic pathway.     

Intramolecular esters of alginic acid

The intramolecular ester (lactone) of alginic acid and of the polyuronide obtained on its fractionating were synthesized, and the effects of temperature and reaction duration on the number of ester groups formed in the polymer were studied.     

Percycloalkylated cyclohexanes: attempted synthesis of a trispropellane

The acid catalyzed rearrangement of two cyclohexanols of spiroannelated four-membered rings has been studied. In accordance with molecular mechanics calculations, far-reaching reorganizations with formation of unsaturated hexacyclic systems, including a fully cycloalkylated cyclohexene with a bispropellane partial structure, were observed. Attempts to convert this bispropellane to a trispropellane failed.     

Asymmetric synthesis of (+)-1-epiaustraline and attempted synthesis of australine

A diastereoselective synthesis of the pyrrolizidine alkaloid, (+)-1-epiaustraline has been achieved via a diastereoselective syn-dihydroxylation of a pyrrolo[1,2-c]oxazol-3-one precursor that was readily prepared by a RCM reaction. Attempts to extend this methodology to the synthesis of australine were not successful since the final pyrrolidine ring closure to produce the desired pyrrolizidine of the target molecule was not productive.     

Intramolecular cation-pi interaction in organic synthesis

Controlling molecular conformation is a significantly important issue in a wide variety of organic reactions because the ground state structure is significantly responsible for the transition one. As observed in enzymes and proteins, the cation-pi interaction plays a key role in the formation of the tertiary structure and the biochemical processes. Therefore, the cation-pi interaction would be a promising conformation-controlling tool not only in large molecules, but also in small molecules due to its stronger interaction force. This article describes the utility of the intramolecular cation-pi interaction in various organic syntheses with evidence for the existence of the cation-pi interactions.     

Stereoselective total synthesis of sporiolide B and attempted synthesis of sporiolide A

A simple and efficient stereoselective total synthesis of sporiolide B and attempted synthesis of sporiolide A, from epichlorohydrin, using asymmetric synthetic approach is reported. The key reactions involved are Sharpless epoxidation, Jacobsen reaction, syn-allylation, Yamaguchi esterification, and Grubbs ring-closing metatheses reaction to result in the macrocyclic ring system.     

Intramolecular direct arylation in the synthesis of fluorinated carbazoles

The amination of 2-chloroanilines with aryl bromides and subsequent intramolecular direct arylation can be exploited in the synthesis of a range of fluorinated carbazoles, where the fluorine substituent can be introduced via the aniline, the aryl bromide or both substrates. Depending on substitution patterns, the two steps can either be performed in tandem in one-pot under microwave heating conditions or else require a two pot approach.     

Intramolecular cyclization ofgem-benzylaminoallylcyclohexane under the action of sulfuric acid

When treated with 855 sulfuric acid at 85°C, gem-benzylaminoallylcyclohexane is converted to spiro[tetrahydrobenz-2-azepine-3-cyclohexane], while at 20°C or in boiling chloroform 3,4,5,6-tetrahydro-3-benzyl-6-methylspiro[1,2,3-oxathiazine-2,2-dioxide-4-cyclohexane] is formed as the major product. The second compound is cleaved by alcohol solution of alkali to 1-benzyl-4-methylspiro[azetidine-2-cyclohexane].Russian University of International Friendship, Moscow 117198. School of Chemistry, Industrial University of Santander, Bucaramanga, A. A. 678, Colombia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 223–227, February, 1999.     

Intramolecular Prins cyclisations for the stereoselective synthesis of bicyclic tetrahydropyrans

Methyl (4E,7R)-7-hydroxyoctanoate was prepared in 71% yield from ethyl (R)-3-hydroxybutanoate and on reaction with a series of aldehydes in the presence of TMSOTf gave bicyclic oxygen heterocycles in good yields and with the creation of three new stereogenic centres in a single pot.     

Intramolecular oxidative C-H coupling for medium-ring synthesis

An oxidative C-H coupling is described for medium-ring synthesis.     

Intramolecular cyclization of cycloalkene carboxylic acid chlorides

Thermal cyclization of cyclooctene-4-yl-carboxylic acid chloride (5) and cycloheptene-4-yl-carboxylic acid chloride (10) yielded mixtures of mainly endo and exo 2-chlorobicyclo[3.3.1]nonane-9-one (7 and 8), and mixtures of endo and exo 2-chlorobicyclo[3.2.1]octane-8-one (12 and 13), respectively. AlCl₃-catalyzed cyclization of 10 gave the same product composition as the uncatalyzed reaction. In the AlCl₃-catalyzed cyclization of 5 considerable amounts of bicyclo[3.3.1]non-2-en-9-one (6) and exo 3-chlorobicyclo[3.3.1]nonane-9-one (9) were obtained in addition to 7 and 8.     

The attempted stereoselective synthesis of chiral 2,2′-biindoline

The attempted first stereoselective synthesis of 2,2′-biindoline using a metathesis-Sharpless asymmetric dihydroxylation strategy results in the synthesis of the heterocycle in poor to modest stereoselectivity. Attempts to improve the ee by varying the heteroatom protecting groups in key intermediates did not enhance the outcome of the Sharpless AD reaction. Therefore a limitation of this AD reaction is the use of 1,4-substituted but-2-enes where these substituents are ortho-substituted aromatics.     

Intramolecular hydrogen bonding as a synthetic tool to induce chemical selectivity in acid catalyzed porphyrin synthesis

A straightforward procedure based on the formation of intramolecular hydrogen bonds to impart selectivity in the preparation of multi-functionalized porphyrins has been developed. To illustrate the concept, the synthesis of a biomimetic artificial photosynthetic model able to undergo electron and proton transfer reactions upon irradiation is reported.     

Structure of an unsymmetrical isomer from the attempted synthesis of 1,8-dicyclooctatetraenylnaphthalene.

Attempted synthesis of 1,8-dicyclooctatetraenylnaphthalene (1) by the palladium(0)-catalyzed coupling of 1,8-dibromonaphthalene with cyclooctatetraenyltrimethylstannane afforded a single unsymmetrical isomer of 1 in 88% yield. Two-dimensional NMR methods and spectral synthesis were employed to assign the structure of the isomer (2). AM1 geometry-optimized structures of 2 and its isomers showed that the unexpected unsymmetrical structure of 2 results from the minimization of repulsive inter-ring H-H interactions. Compound 2 is postulated to arise via tandem [2 + 2] cycloaddition and 6 pi --> 4 pi + 2 sigma electrocyclization reactions of 1.     

Mechanistic studies in the attempted synthesis of 5,5-dimethyl-2-isopropylidene-1,3-cyclohexanedione

In contrast to the corresponding cyclopentanedione derivative, 5,5-dimethyl-2-isopropyl-2-phenylsulfinyl-1,3-cyclohexanedione (3) does not undergo the expected cis-elimination of phenylsulfenic acid on warming in CH₂Cl₂ to afford the title compound 1, but instead gives an equimolar mixture of 5,5-dimethyl-2-(1 ′-isopropyl-4′,4′-dimethyl-2′,6′-dioxocyclohexyl)-2-isopropyl-1, 3-cyclohexanedione (9) and S-phenyl benzenethiosulfonate (10). These products result from dimerization of the 4,4-dimethyl-1-isopropyl-2,6-dioxocyclohexylradical (7) andthephenylsulfinyl radical (8), respectively. Diploma Thesis, University of Hamburg, 1990.     

Intramolecular general acid catalysis in the aminolysis of beta-lactam antibiotics

The rate of aminolysis of benzylpenicillin and cephaloridine by hydroxylamine, unlike other amines, shows only a first order dependence on amine concentration. The rate enhancement compared with that predicted from a Bronsted plot for other primary amines with benzylpenicillin is greater than 10(6). This is much more than an alpha-effect and is compatible with rate-limiting formation of the tetrahedral intermediate due to a rapid intramolecular general acid catalysed breakdown of the intermediate. For cephaloridine, the rate enhancement is greater than 10(4) which demonstrates that beta-lactam C-N bond fission and expulsion of the leaving group at C3' are not concerted.