Synthetic transformations of higher terpenoids: XXIII. Synthesis of diterpenoid-based dihydroisoindolones

Vilsmeier-Haak reaction of phlomisoic acid methyl ester gave a mixture of 15- and 16-formyllabdanoids. In addition, methyl 2-formyldodecahydrophenanthro[1,2-b]furan-6-carboxylate was isolated, and its structure was determined by X-ray analysis. Reductive amination of 16-formyllabdanoid with benzylamine or α-amino acid methyl esters led to the formation of labdanoid furfurylamines which reacted with maleic anhydride to produce N-substituted 4-oxo-10-oxa-3-azatricyclo[5.2.1.0^1,5]dec-8-ene-6-carboxylic acids. Acylation of labdanoid furfurylamines with (E)-but-2-enoyl chloride afforded the corresponding unsaturated amides which were converted into 10-oxa-3-azatricyclo[5.2.1.0^1,5]dec-8-en-4-ones via intramolecular Diels-Alder reaction. Treatment of the oxa adducts with boron trifluoride-diethyl ether complex gave dihydroisoindol-1-one derivatives containing a diterpene fragment.     

Synthetic transformations of higher terpenoids: XX. Synthesis and transformations of diterpene ureido esters

Lossen rearrangement of N-hydroxymaleopimaric acid amide p-toluenesulfonate in the presence of amines in methanol led to the formation of the corresponding diterpene ureido esters with high regio- and stereoselectivity. Treatment of the resulting ureides with phosphoryl chloride gave cyclic amidines via intramolecular ring closure. Substituted hydantoins were obtained by reactions of the ureido esters with glyoxal in acid medium, and their treatment with sodium ethoxide in ethanol afforded compounds of the naphtho[1,2-h]-quinazoline series.     

Synthetic transformations of higher terpenoids: XIV. Synthesis of pyrrololabdanoids from lambertianic acid

Treatment of lambertianic acid methyl ester with lead tetraacetate gave terpenoid 2,5-diacetoxydihydrofuran which reacted with primary amines to yield 3-terpenyl-substituted pyrrol-2(5H)-ones; the reaction with hydrazine led to the corresponding pyridazine derivative. The obtained furanoterpenoids underwent oxidative methoxylation by the action of N-chlorobenzenesulfonamide or N-bromosuccinimide in methanol. 2,5-Dimethoxydihydrofurans thus formed were smoothly converted into 3-substituted furan-2(5H)-one in acid medium. Hydrogenation of 2,5-dimethoxydihydrofurans, followed by treatment with amines, gave 1,3-disubstituted pyrroles.     

Synthetic transformations of higher terpenoids: XXIV. Synthesis of cyanoethyl derivatives of lupane triterpenoids and their transformation into 1,2,4-oxadiazoles

Cyanoethylation of lupane triterpenoids was performed. Amide oximes of 3β-O-(2-cyanoethyl)-betulinic acid methyl ester and 3β-O-acetyl-28-O-(2-cyanoethyl)betulin and the corresponding O-[2-(1,2,4-oxadiazol-3-yl)ethyl] lupane derivatives were obtained.     

Synthetic transformations of higher terpenoids: XXXVI. Synthesis of furanolabdanoid glycoconjugates with a 1,2,3-triazole linker

Procedures have been developed for the synthesis of 16-[(propargyloxy)methyl]- and 7- and 18-(propargyloxy)labda-8(9),13,14-trienes from phlomisoic acid. Copper-catalyzed cycloaddition of the labdanoid alkynes to azido derivatives of α-D-glucose, D-galactose, D-xylose, and L-arabinose afforded the corresponding N-glycosyl-1,2,3-triazole conjugates.     

Synthetic transformations of higher terpenoids: XXII. Reactions of lambertianic acid derivatives with organozinc reagents obtained from ethyl bromoalkanoates

Reactions of 16-cyanomethyllambertianate with organozinc reagents obtained from ethyl esters of α-bromoacetic, α-bromopropionic, and α-bromobutyric acids gave the corresponding enaminoesters, β-ketoesters, and β-hydroxyesters of labdanoids whose yield depended on the reaction conditions and the structure of the α-bromoester. By Reformatsky reaction of 16-formylmethyllambertianate with α-bromoesters of carboxylic acids stereoisomeric β-hydroxyesters of labdanoids were synthesized.     

Synthetic transformations of higher terpenoids: XVI. Synthesis of decahydronaphtho[1,2-g]indoles from lambertianic acid

Oxidative methoxylation of 8,17-isopropylidenedioxy derivative of lambertianic acid methyl ester with N-chlorobenzenesulfonamide in methanol, followed by hydrogenation over Raney nickel, gave rise to a 2,5-dimethoxytetrahydrofuran fragment which was converted into N-substituted pyrrole ring by the action of amines in acetic acid. The subsequent removal of the acetonide protection and periodate cleavage of the diols thus formed resulted in the formation of 17-nor-8-oxo derivatives, and the latter underwent smooth cyclization to decahydronaphtho[1,2-g]indoles in acid medium.     

Synthetic transformations of higher terpenoids: XII. Transformation of lambertianic acid into 14,16-epoxyabietane diterpenoids

Hydroxylation of lambertianic acid with potassium permanganate in alkaline medium afforded 15,16-epoxy-8α,17-dihydroxy-13(16),14-labdadienoic acid which was oxidized with periodic acid to the corresponding 8α-hydroxy aldehyde, and the latter underwent smooth cyclization in acid medium to give diterpenoid of the 14,16-epoxyabietane series.     

Synthetic transformations of higher terpenoids: XIV. Heterocyclization reactions of 15,16,18-ricarboxylabdadiene. New nitrogen-containing diterpenoids

The oxidation of methyl lambertianate with Jones’ reagent formed the corresponding anhydride which reacted with amines to form N-substituted terpenoid maleimides. New maleimides demonstrated high activity and stereoselectivity in the Diels-Alder reaction with cyclopentadiene. The condensation of the diterpenoid anhydride with hydrazines led to the formation of derivatives of 3,6-dioxo-1,2,3,6-tetrahydropyridazines of labdane type.     

Synthetic transformations of higher terpenoids: XXXII. Synthesis of 16-alkenyl-substituted labdatrienes by oxidative coupling of methyl phlomisoate with alkenes

Reactions of methyl phlomisoate with methyl acrylate, phenyl acrylate, methyl vinyl ketone, phenyl vinyl ketone, or N-substituted acrylamides catalyzed by Pd(OAc)₂ in the presence of Cu(OAc)₂, p-benzoquinone in the mixture of propionic acid and acetonitrile proceed regio- and stereoselectively with the formation of (E)-16-vinyl labdatrienoates. The oxidative coupling under these conditions of the methyl phlomisoate with styrene results in a mixture of 15,16-distyryl-, 16-styryl-, and 16-(1-phenylvinyl)-derivatives of furanolabdanoid.     

Synthetic transformations of higher terpenoids: XVII. Intramolecular cyclization of N-furfuryl amides of the labdane series

16-(Benzylaminomethyl)lambertianic acid methyl ester reacts with 2-methylprop-2-enoyl chloride to give unsaturated amide which readily undergoes intramolecular [4 + 2]-cycloaddition with formation of terpenoid derivatives of 10-oxa-3-azatricyclo[5.2.1.0^1,5]decenone. Acetylation of lambertianic acid methyl ester with acetic anhydride occurs preferentially at the 2-position of the furan ring and is accompanied by migration of the exocyclic double bond. Reductive amination of 16-acetyl-15,16-epoxylabda-8(9),13,14-triene and subsequent reaction of the resulting amine with 2-methylprop-2-enoyl chloride give intramolecular cyclization products in high yield without isolation of intermediate furfurylacryloyl derivative. Reactions of methyl 16-(benzylaminomethyl)-15,16-epoxylabda-8(9),13,14- and -8(17),13,14-trien-18-oates with maleic anhydride lead to the formation of the corresponding 10-oxa-3-azatricyclo[5.2.1.0^1,5]dec-8-ene-6-carboxylic acid derivatives as mixtures of diastereoisomers.     

Synthetic transformations of higher terpenoids: XXVIII. Diels-Alder reactions of 16-(trimethylsiloxybutadienyl) labdanoids

15,16-Epoxy-16-(3-trimethylsiloxybuta-1,3-dien-1-yl)labdanoids were synthesized, and their reactions with cyclic dienophiles (1,4-benzoquinone, 1,4-toluquinone, 2-bromo-6-methyl-1,4-benzoquinone, and N-methylmaleimide) were studied. The reactions with unsymmetrically substituted benzoquinones were not selective. Methods for the preparation of hybrid compounds containing furan diterpenoid and substituted naphthoquinone, octahydroisoindoletrione, or hexahydroisoindoledione fragments were proposed.     

Synthetic transformations of higher terpenoids: XXIX. Gold catalyzed cycloisomerization of propargylaminomethyl substituted and propargyloxymethyl substituted furanolabdanoids

16-Propargylaminomethyl substituted and 16-propargyloxymethyl substituted furanolabdanoids were synthesized, which under the action of AuCl₃ in acetonitrile underwent cycloisomerization forming 7-hydroxyisoindolines or 7-hydroxydihydroisobenzofurans substituted by a terpenoid fragment.     

Synthetic transformations of higher terpenoids: XV. Transformations of azlactone derived from 16-formyllambertianic acid methyl ester

Condensation of 16-formyllambertianic acid methyl ester with hippuric acid gave methyl 15,16-epoxy-16-[(4Z)-5-oxo-2-phenyl-4,5-dihydrooxazol-4-ylidenemethyl]labda-8(20),13(16),14-trien-19-oate which underwent ready transformation into 2-benzoylamino-3-(2-furyl)acrylic acid of the labdanoid series. Reactions of the diterpenoid azlactone with amines and α-amino acid esters led to the formation of the corresponding carbamoylvinylbenzamides and N-(2-benzoylaminoacryloyl) amino acid esters, and furylacrylic acid hydrazides were formed in reactions with hydrazines. Cyclization of the N′-phenylhydrazide by the action of 1 M aqueous sodium hydroxide gave the corresponding 1,2,4-triazin-6-one. By treatment of the azlactone with aqueous ammonia on heating, 4-substituted 2-phenyl-4,5-dihydroimidazol-5-one was obtained.     

Synthesis of optically active amphiphilic tetrathiafulvalene derivatives

The synthesis and characterization of novel chiral tetrathiafulvalenes bearing two long alkyl chains at one end of the π-electron rich unit and different functional groups—ester, acid or thiolate—at the other extreme is described. The synthetic method requires the preparation of 1,3-dithiol derivatives with two stereogenic centers. Different routes and reaction conditions were explored to form these compounds, whose optimized synthesis involved the nucleophilic substitution of a chiral bromo methylene derivative with tetrabutylammonium bis(2-thioxo-1,3-dithiole-4,5-dithiolate)zincate. The tetrathiafulvalenes were prepared by coupling the 1,3-dithiol derivative with 4,5-bis(methoxycarbonyl)-1,3-dithiol-2-one or 4,5-bis(2-cyanotehylthio)-1,3-dithiol-2-thione. The products were fully characterized, including by circular dichroism spectroscopy, which confirmed their optical activity. They are promising candidates to be used as building blocks in supramolecular materials for molecular electronics, to produce systems with unique electrical, magnetic or optical properties that stem from their chirality.     

Synthesis of optically active verrucarinic acid derivatives

Two syntheses of verrucarinic acid highlighting an oxidative cleavage of hydroxysulfides and use of mandelate esters for chromatographic resolution are reported.     

Tautomerism of anthraquinones: V. 1,5-Dihydroxy-9,10-anthraquinone and its substituted derivatives

1,5-Dihydroxyanthraquinone and its substituted derivatives are capable of existence in the states structurally described as 9,10-, 1,10-, and 1,5-quinoid tautomerism, and as rotational isomerism involving a cleavage of intramolecular hydrogen bond. 1,5-Quinoid tautomers are characteristic only of substituted derivatives, and also appear in some metal complexes. The considerable color changes on introducing into the 1,5-dihydroxy-anthraquinone methyl, methoxy, and sulfo groups are caused by the shift in tautomeric and conformer equilibria.     

Tautomerism of anthraquinones: IV. 1-Hydroxy-9,10-anthraquinone and its substituted derivatives

1-Hydroxyanthraquinone and its substituted derivatives exist as equilibrium mixtures of four tautomers and rotational isomers. Their anions have 9,10-and 1,10-quinoid structures. Each tautomer or conformer is characterized by a single π₁,π* band in the electronic absorption spectrum.