Chiral synthons from campholenaldehyde: enantiospecific synthesis of diquinane and linear triquinanes

Enantiospecific syntheses of diquinane and linear triquinanes were accomplished, starting from the readily available alpha-campholenaldehyde employing a Nazarov reaction as the key step. (C) 2010 Elsevier Ltd. All rights reserved.

Enantiospecific total synthesis of aciphyllene

Enantiospecific total synthesis of the sesquiterpene aciphyllene and its three epimers have been described starting from the readily available monoterpene (R)-limonene employing an intramolecular type II carbonyl ene reaction as the key step. (C) 2010 Elsevier Ltd. All rights reserved.

Enantiodivergent Formal Total Synthesis of Aspercyclide C from L-(+)-Tartaric Acid

The enantiodivergent formal syntheses of both enantiomers of aspercyclide C is accomplished. Starting from L-(+)-tartaric acid, the key protected allylic alcohol, (3R,4R)-4-(methoxy-methoxy) non-1-en-3-ol is prepared, and is then elaborated into both enantiomers of 3-(4-methoxybenzyl)oxy]non-1-en-4-ol via Mitsunobu inversion. Esterification with a known biaryl acid, followed by ring-closing metathesis and deprotection completes the syntheses.

First total synthesis of a natural thapsane

A stereospecific first total synthesis of a natural thapsane 1, from the readily available cyclogeraniol 8, is described.

A regio and stereospecific radical annulation route to chiral tricyclo[4.3.1.o3,7]decane (isotwistane) system1 synthesis of (+)-10-α-Naphthyl-5-epi-Pupukean-9-one

Contrary to that of phenyl derivative 1 the radical 4 adds to radicophiles in an inter- followed by intra-molecular radical Michael addition (radical annulation), furnishing a novel route to chiral isotwistanes 5.

Synthetic studies in aromatic hemiterpenes of natural origin, Part 5: Synthesis of 6-acetyl-2,2-dimethyl-8-methoxychromene via benzylic oxidation route

The synthesis of 6-acetyl-2,2-dimethyl-8-methoxychromene (lc), a naturally occurring isomer of encecalin (la)h~s been described startilag from 2,2,6- trimethyl-8-methoxyclaromene (2e) which was obtained from creosol (4) in two steps involving condensation of the phenol with malic acid to the coumarin (3), followed by Grignard reaction with CHaMgI. The transformation of (2e) to the natural product (lc) was effeeted by oxidative dehydrogenation by DDQ of the 6-meth~r function to the formyl group (2f), Grignard reaction to the carbinol (2g) and finally its oxidation to the acetyl moiety (lc), the sequence of the essential steps schematically summarised as : Ar-CHs --* Ar-CHO --* Ar-CH (OH) CHs --* Ar---COCHs.

Total synthesis of enokipodins A-D and cuparene-1,4-diol

A Claisen rearrangement and RCM reaction based sequence has been developed for total synthesis of the antifungal sesquiterpenes enokipodins A-D and cuparene-1,4-diol starting from 2,5-dimethoxy-4-methylhydroquinone.

One pot synthesis of polycyclic oxygen aromatics. Part III mechanism of formation

Reaction of 6-Image -butyl-1-bromomethyl-2-(2-tetrahydropyranyloxy)-naphthalene2c with tetrachlorocatechol (TCC) in acetone in presence of K2CO3 gave diastereomers 6c and 7c. A mechanism (Scheme-1) invoking the base induced cleavage of the pyranyl ether 2 to 1,2-naphthoquinone-1-methide 8 as the first step has been postulated. The cleavage of the pyranyl ether linkage in 2 to give dimers 4 and 5 of 1,2-naphthoquinone-1-methide has been demonstrated with different bases. 1,2-Naphthoquinone-1-methide 8, thus generated, undergoes Michael addition with TCC followed by elimination of chloride ions to give a diketone, which further undergoes aldolisation with acetone to give diastereomers 6 and 7. Michael reaction of 8, generated Image from pyranyl ethers 2a-c, with tetrabromocatechol (TBC) under similar-reaction conditions gave the expected monobromo compounds 6h, 6i, 6k, 7n, 7n and 7q. The last step in the proposed mechanism, Image ., aldolisation has also been demonstrated using different ketonic solvents. Thus, reaction of 2a-c with TCC/TBC in diethyl ketone/methyl ethyl ketone under similar reaction conditions gave the expected compounds 6 and 7.

Oxidation of Quinolinols - Synthesis of Spirodienones Containing Nitrogen

Reaction of 6-quinolinol with formaldehyde and sodium sulphite gives the bisquinolinol (1b). Similar reaction of 6-quinolinol with sodium 2-hydroxy1-naphthylmethanesulphonate gives 1c. Oxidation of 1b with K3Fe(CN)6 or KOBr gives the spiroquinolinone 2b, while oxidation of 1c with K3Fe(CN)6 results in the formation of spirodienones 2c and 2d, and the dispiroketones 7b and 7c. Oxidation of 1c with DDQ, however, results in only the spirodienones 2c and 2d. The spirodienone 2d and the bromospiroquinolinone 2e are formed in the reaction of 1c with KOBr.

Roofed polyquinanes: synthesis and electronic structure

Starting from readily available norbornenobenzoquinone 7 and employing a photothermal metathesis reaction as the main strategy, novel "roofed" polyquinane bisenones 3 and 13 have been synthesized. Among these, the former is potentially serviceable for further elaboration to dodecahedrane 1. Catalytic hydrogenation of 3 provided the dione 12, which fully inscribes the circumference of dodecahedrane sphere. The "roofed" C-16-bisenone 3 has been successfully annulated to C19-bisenone 24 and C19-trisenone 26 by employing the Greene methodology and Pauson-Khand reaction, respectively. The molecular structures of 3 and 13 were computed using molecular mechanics and semiempirical MO methods. The nonbonded distances between the double bonds vary strongly with the method employed. The interactions between the pi-MO's were, therefore, probed by means of photoelectron (PE) spectroscopy. Comparison with the PE spectra of a series of model systems with increasing complexity enabled an unambiguous assignment of the observed peaks. The symmetric and antisymmetric combinations of the pi-MO's of the enone moieties of 3 and 13 show large splittings, characteristic of propano-bridged systems in which through-space and through-bond effects act in concert.

Stereospecific total synthesis of (±)-albene via a prochiral precursor

The total synthesis of racemic albene 2 via the prochiral precursor 3, using a stereoselective Claisen rearrangement and an intramolecular diazoketone cyclopropanation as key reactions, is described.