Acid-Catalyzed Rearrangements of 5,6-exo-Epoxy-7-oxabicyclo[2.2.1]hept-2-yl Derivatives. Migratory Aptitudes of Acyl vs. Alkyl Groups in Wagner-Meerwein Transpositions

In the presence of HSO₃F/Ac₂O in CH₂CL₂, 2-exo- and 2-endo-cyano-5,6-exo-epoxy-7-oxabicyclo[2.2.1]hept-2-yl acetates ( 6a , b ) gave products derived from the epoxide-ring opening and a 1,2-shift of the unsubstituted alkyl group (σ bond C(3)–C(4)). In contrast, under similar conditions, the 5,6-exo-epoxy-7-oxabicyclo[2.2.1]heptan-2-one ( 6c ) gave 5-oxo-2-oxabicyclo[2.2.1]heptane-3,7-diyl diacetates 20 and 21 arising from the 1,2-shift of the acyl group. Acid treatment of 5,6-exo-epoxy-2,2-dimethoxy-7-oxabicyclo[2.2.1]heptane ( 6d ) and of 5,6-exo-epoxy-2,2-bis(benzyloxy)-7-oxabicyclo[2.2.1]heptane ( 6e ) gave minor products arising from epoxide-ring opening and the 1,2-shift of σ bond C(3)–C(4) and major products ( 25 , 29 ) arising from the 1,3-shift of a methoxy and benzyloxy group, respectively. Under similar conditions, 5,6-exo-epoxy-2,2-ethylenedioxy-7-oxabicyclo[2.2.1]heptane ( 6f ) gave 1,1-(ethylenedioxy)-2-(2-furyl)ethyl acetate ( 32 , major) and a minor product 33 , arising from the 1,2-shift of σ bond C(3)–C(4). The following order of migratory aptitudes for 1,2-shifts toward electron-deficient centers has been established: acyl > alkyl > alkyl α-substituted with inductive electron-withdrawing groups. This order is valid for competitive Wagner-Meerwein rearrangements involving equilibria between carbocation intermediates with similar exothermicities.     

The electron-releasing homoconjugated carbonyl group. Application to the total syntheses of 3-deoxy-, 4-deoxy-hexose, lividosamine and derivatives

The regioselective electrophilic addition of benzeneselenyl bromide to (−)-(1S,4S)-7-oxabicyclo[2.2.1]-hept-5-en-2-one were exploited to develop efficient syntheses of methyl 3-deoxy--D-arabino-hexofuranoside and 4-deoxy-D-lyxo-hexopyranose. Similarly, D-lividosamine (3-deoxy-D-glucosamine) was derived from (+)-(1R,4R)-7-oxabicyclo[2.2.1]hept-5-en-2-one.     

Structural analysis of three methyl N-phosphorylated 5,6-dihydroxy-2-azabicyclo[2.2.1]heptane-3-carboxylates

Both exo and endo isomers of (±)-methyl N-diphenylphosphoryl-2-azabicyclo[2.2.1]hept-5-ene-3-carboxylate and (±)-methyl N-diphenylphosphoryloxy-2-azabicyclo[2.2.1]hept-5-ene-3-carboxylate were dihydroxylated with OsO₄. The unexpected formation of (±)-methyl 5,6-dihydroxy-N-diphenylphosphoryl-2-azabicyclo[2.2.1]heptane-3-endo-carboxylate from (±)-methyl N-diphenylphosphoryloxy-2-azabicyclo[2.2.1]hept-5-ene-3-endo-carboxylate is discussed based on NMR analyses and experimental observations. The two N-diphenylphosphoryl dihydroxybicycles are analyzed in terms of their crystalline structure by X-ray crystallography.     

Synthesis of (+)-1,3:2,5-dianhydroviburnitol ((+)-(1R,2R,3S,5R,6S)-4,7-dioxatricyclo[3.2.1.03,6]octan-2-ol)

Epoxidation of (?)-(1R,2R,4R)-2-endo-cyano-7-oxabicyclo[2.2.1]hept-5-en-2-exo-yl acetate ((?)-5) followed by saponification afforded (+)-(1R,4R,5R,6R)-5,6-exo-epoxy-7-oxabicyclo[2.2.1]heptan-2-one ((+)-7). Reduction of (+)-7 with diisobutylaluminium hydride (DIBAH) gave (+)-1,3:2,5-dianhydroviburnitol ( = (+)-(1R,2R,3S,4R,6S)-4,7-dioxatricyclo[3.2.1.0^3,6]octan-2-ol; (+)-3). Hydride reductions of (±)-7 were less exo-face selective than reductions of bicyclo[2.2.1]heptan-2-one and its derivatives with NaBH₄, AlH₃, and LiAlH₄ probably because of smaller steric hindrance to endo-face hydride attack when C(5) and C(6) of the bicyclo-[2.2.1]heptan-2-one are part of an exo oxirane ring.     

Interaction between Oxygen Lone-Pair Orbitals of Ether and α,β-Unsaturated Ketone Functions in 3,5,6-Trimethylidene-7-oxabicyclo[2.2.1]heptan-2-one and 3,6-Dimethylidene-7-oxabicyclo[2.2.1]heptane-2,5-dione: A PE-Spectroscopic Investigation

Controlled ozonolysis of 2,3,5,6-tetramethylidene-7-oxabicyclo[2.2.1]heptane ( 1 ) afforded 3,5,6-trimethylidene-7-oxabicyclo[2.2.1]heptan-2-one ( 2 ). Ozonolysis of 2 gave a 1:1 mixture of 3,5-dimethylidene-7-oxa-bicyclo[2.2.1]heptane-2,6-dione ( 3 ) and 3,6-dimethylidene-7-oxabicyclo[2.2.1]heptane-2,5-dione ( 4 ). The He(Iα) photoelectron (PE) spectra of 2 and 4 have been recorded. Comparison with the PE data of related systems, and with the result of ab initio STO-3G calculations, confirm the existence of significant through-bond interactions between the oxygen lone-pair orbitals n(CO) of the carbonyl functions and n(O) of the O(7) ether bridge.     

Highly Stereoselective Total Syntheses of 2,5-Anhydro-4-deoxy-D-ribo-hexonic Acid and of (1S)-1-C-(6-amino-7H-purin-8-yl)-1,4-anhydro-3-deoxy-D-erythro-pentitol (= cordycepin C)

Highly regio- and stereoselective monohydroxylation of the C?C bond of (+)-7-oxabicyclo[2.2.1]hept-5-en-2-one ( 8 ) was achieved via LiAlH₄ reduction of the corresponding 5,6-exo-epoxy dimethyl acetal 9 . The reaction gave exclusively (–)-(1R, 2R, 4S)-6,6-dimethoxy-7-oxabicyclo[2.2.1]heptan-2-exo-ol ( 10 ) which was transformed into 2,5-anhydro-3-O-benzyl-4-deoxy-D -ribo-hexonic acid ( 15 ) and 2,5-anhydro-4-deoxy-D -ribo-hexonic acid ( 6 ) via ozonolysis of (–)-(1R, 4S, 6R)-6-exo-benzyloxy-2-{[(tert-butyl)dimethylsilyl]oxy}-7-oxabicyclo[2.2.1]hept-2-ene ( 14 ). Cordycepin C ( 5 ) was derived from 6 and 4,5,6-triaminopyrimidine using CsF/DMF to generate the adenine heterocycle.     

Cyclodimerization of 1-(Dimethoxyniethyl)-5,6-dimethylidene-7-oxa-bicyclo[2.2.1]hept-2-ene Induced by Nonacarbonyldiiron. Crystal Structure of (1RS, 2SR, 3RS, 4RS, 4aRS, 9aSR)- Tricarbonyl[C, 2,3, C-η-(1,4-epoxy-1,5-bis(dimethoxymethyl)-2,3-dimethylidene-1,2,3,4,4a,9,9a,10-octahydroanthracene)]iron

The transition-metal-carbonyl-induced cyclodimerization of 5,6-dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene is strongly affected by substitution at C(1) While 5,6-dimethylidene-7-oxabicyclo[2.2.1]hept–2-ene-l-methanol ( 7 ) refused to undergo [4 + 2]-cyclodimerization in the presence of [Fe₂(CO)⁹] in MeOH, 1-(dimethoxymethyl)-5,6-di-methylidene-7-oxabicyclo[2.2.1]hept-2-ene ( 8 ) led to the formation of a 1.7:1 mixture of ‘trans’ ( 19, 21, 22 ) vs. ‘cis’ ( 20, 23, 24 ) products of cyclodimerization together with tricarbonyl[C, 5,6, C-η-(l-(dimethoxymethyl)-5,6-di-methylidenecyclohexa-1,3-diene)]iron ( 25 ) and tricarbonyl[C,3,4, C-η-(methyl 5-(dimethoxymethyl)-3,4-di-methylidenecyclohexa-1,5-diene-l-carboxylate)]iron ( 26 ). The structures of products 19 and of its exo ( 21 ) and endo ( 22 ) [Fe(CO)₃(1,3-diene)]complexes) and 20 (and of its exo ( 23 ) and endo (24) (Fe(CO)₃(1,3-diene)complexes) were confirmed by X-ray diffraction studies of crystalline (1RS, 2SR, 3RS, 4RS, 4aRS, 9aSR)-tricarbonyl[C, 2,3, C-η-(1,4-epoxy-1,5-bis(dimethoxymethyl])-2,3-dimethylidene-1,2,3,4,4a,9,9a,10-octahydroanthracene)iron ( 21 ). In the latter, the Fe(CO)₃(1,3-diene) moiety deviates significantly from the usual local C_s symmetry. Complex 21 corresponds to a ‘frozen equilibrium’ of rotamers with η-alkyl, η³-allyl bonding mode due to the acetal unit at the bridgehead centre C(1).     

Zum Komplexbildungsverhalten der 5,6-Dihydroxy-7-oxa-bicyclo[2.2.1]heptan-2,3-dicarbonsäure gegenüber 3 d-Übergangsmetallen

Complex Formation of 5,6-Dihydroxy-7-oxa-bicyclo[2.2.1]heptane-2,3-dicarboxylic Acid with 3 d-Transition Elements Binary carboxylate complexes of bivalent 3 d-transition metal ions with 5-exo,6-cis-dihydroxy-7-oxabicyclo[2.2.1]heptane-2-exo,3-cis-dicarboxylic acid ( 2 ) have been synthesized in aqueous solution and characterized by elementary analysis, infrared and electronic spectra and magnetic susceptibility measurements. The coordination compounds have been found to undergo thermal decomposition with loss of water molecules, followed by the organic ligand to give metal oxides. The stability constants of the complexes have been determined by potentiometric measurements. It could be shown by X-ray analysis, that the dicarboxylate anion of 2 has different coordination behaviour in complexes [NiL²(H₂O)₃] · H₂O ( 2 c ) and [CuL²(H₂O)₂] · 2 H₂O ( 2 d ), respectively. In 2 c it acts as a tridentate chelating ligand forming together with three water molecules an only slightly distorted octahedral coordination sphere and its hydroxyl groups are coordinatively inactive. In 2 d , however, the oxygen atom of one hydroxyl group is included in coordination and by its interaction with a Cu atom of a neighboring molecule a polymeric chain structure is built up in the crystal. Two corners of the tetragonally extended coordination octahedron are occupied by water molecules. In both complexes the molecular packing is stabilized by a network of hydrogen bonds in which also the crystal water molecules are included.     

Chemo- and Stereoselective Coordination of 5,6-Dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene by d8- and d6-Metal Carbonyls. Diels-Alder reactivity of Dienes Perturbed by Remote Olefin Complexation

The endocyclic double bond C(2), C(3) in 5,6-dimethylidene-7-oxabicyclo[2.2.1]-hept-2-ene ( 1 ) can he coordinated selectively on its exo-face before complexation of the exocyclic s-cis-butadiene moiety. Irradiation of Ru₃(CO)₁₂ or Os₃(CO)₁₂ in the presence of 1 gave tetracarbonyl [(1R,2R, 3S,4S)-2,3-η-(5,6-dimethylidene-7-oxabicyclo[2.2.1]-hept-2-ene)]ruthenium ( 6 ) or -osmium ( 8 ). Similarly, irradiation of Cr(CO)₆ or W(CO)₆ in the presence of 1 gave pentacarbonyl[(1R, 2R, 3S,4S)-2,3-η-(5,6-dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene)]chromium (10) or -tungsten (11) . Irradiation of complexes 6 and 11 in the presence of 1 led to further CO substitution giving bed-tricarbonyl-ae-bis[(1R,2R,3S,4S)-2,3-η-(5,6-dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene)]ruthenium ( 7 ) and trans-tetracarbonyl[(1R,2R,3S,4S)-2,3-η-(5,6-dimethylidene-7-oxabicyclo-[2.2.1]hept-2-ene)]tungsten (12) , respectively. The diosmacyclobutane derivative cis-m?-[(1R,3R,3S,4S)-(5,6-dimethylidene-7-oxabicyclo[2.2.1]hepta-2,3-diyl)]bis(tetracarbonyl-osmium) (Os-Os) (9) wa also obtained. The Diels-Alder reactivity of the exocyclic s-cis-butadiene moiety in complexs 7 and 8 was found to be significantly higher than that of the free triene 1 .     

Total asymmetric syntheses of d-lividosamine and 2-acetamido-2,3-dideoxy-d-arabino-hexose derivatives.

The “naked sugar” (+)-(1R, 4R)-7-oxabicyclo[2.2.1]hept-5-en-one((+)-2) has been converted to D-lividosamine ((+)-1: 3-deoxy-D-glucosamine) and derivatives via (+)-2-chloro-2,3-dideoxy-5,6-O-isopropylidene-D-arabino-hexono-1,4-lactone ((+)-33) and (+)-2-azido-2,3-dideoxy-5,6-O-isopropylidene-D-ribo-hexono-1,4-lactone ((+)-34) in a highly stereoselective fashion. Similarly, 2-acetamido-2,3-dideoxy-D-arabino-hexose and derivatives were derived from the “naked sugar” (−)-(1S,4S-7-oxabicyclo[2.2.1]-hept-5-en-2-one ((−)-2) via the double hydroxylation of the C=C double bond in (−)-N-benzyl-N-[(1R,2S,4S)-6-bromo-7-oxabicyclo[2.2.1]hept-5-en-2-endo-yl] amine ((−)-40).     

Ironcarbonyl Complexes of 5,6-Dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene Derivatives. Synthesis of Substituted Tricarbonyl(ortho-quinodimethane)iron Complexes and 2-Indanones

The l-dimethoxymethyl-5,6-dimethyldene-7-oxabicyclo[2.2.1]hept-2-ene ( 9 ) has been prepared. On treatment with Fe₂(CO)₉, the endocyclic double bond C(2)?C(3) was coordinated first giving the corresponding exo-Fe(CO)₄ complex 10 . The latter reacted with Fe₂(CO)₉ and afforded cis-heptacarbonyl-μ-[1RS,2SR,3RS,4SR,5RS,6SR-2,3-η: C5,6,C-η-(1-(dimethoxymethyl)-5,6-dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene)]diiron ( 11 ) as a major product. On heating, 11 underwent deoxygenation of the 7-oxabicyclo[2.2.1]heptene moiety yielding tricarbonyl[C,5,6,C-η-(1-(dimethoxymethyl)-5,6-dimethylidenecyclohexa-1,3-diene)]iron ( 13 ). In MeOH, a concurrent, regioselective methoxycarbonylation was observed giving tricarbonyl[C,3,4,C-η-(methyl 5-(dimethoxymethyl)-3,4-dimethylidenecyclohexa-1,5-diene-1-carboxylate)]iron ( 14 ). Oxidative removal of the Fe(CO)₃ moiety in 13 and 14 did not afford the expected ortho-quinodimethane derivatives but led to CO insertions giving 2,3-dihydro-2-oxo-1Hindene-4-carbaldehyde ( 20 ) and methyl 7-formyl-2-3-dihydro-2-oxo-lH-indene-5-carboxylate ( 21 ), respectively.     

7-氧杂双环[2.2.1]庚-2,3-二甲酸衍生物的合成及其抗HIV活性

以呋喃和顺丁烯二酸酐为原料,经环化反应制得7-氧杂双环[2.2.1]庚-5-烯-2,3-二甲酸酐(3);打开3的酸酐五元环,选择性地进行单酯化反应,合成了一系列7-氧杂双环[2.2.1]庚-3-烷氧羰基-2-甲酸(4a～4d),其结构经1H NMR和MS表征.初步探讨了4的抗HIV构效关系,其中4a的治疗指数与其先导化合物去甲基斑蝥素相当,毒性较之降低.     

Design, synthesis, and 1,3-dipolar cycloaddition of (5R)- [and (5S)]-5,6-dihydro-5-phenyl-2H-1,4-oxazin-2-one N-oxides as chiral (E)-geometry-fixed alpha-alkoxycarbonylnitrones

Optically pure (5R)- [and (5S)]-5,6-dihydro-5-phenyl-2H-1, 4-oxazin-2-one N-oxides [(5R)- and (5S)-2] were designed as chiral (E)-geometry-fixed alpha-alkoxycarbonylnitrones 1. The nitrones (5R)- and (5S)-2 were synthesized by three-step oxidation of (R)- and (S)-phenylglycinols [(R)- and (S)-3], condensation of the resulting (R)- and (S)-2-hydroxylamino-2-phenylethanols [(R)- and (S)-5] with glyoxylic acid, and cyclization of the intermediary nitrones (R)- and (S)-6b. The nitrone (5R)-2reacted with olefins 7-14 under mild conditions to afford the corresponding cycloadducts 15-22 as the main products via the least sterically demanding exo modes. Cycloadduct 30 obtained from (5S)-2 and cyclopentadiene was effectively elaborated to (1S,4S, 5R)-4-benzyloxycarbonylamino-2-oxabicyclo[3.3.0]oct-7-en-3-one (28), the key synthetic intermediate of carbocyclic polyoxin C.     

Total asymmetric syntheses of 3- and 4-deoxy-hexoses and derivatives

(1S,4S)-7-Oxabicyclo[2.2.1]hept-5-en-2-one ((−)-5, a “naked sugar”) has been converted to (−)-(1R,4S,6S)-6-endo-benzyloxy-2-bromo-7-oxabicyclo[2.2.1]hept-2-ene ((−)-12) in a highly stereoselective fashion. Double hydroxylation of the C=C double bond of (−)-12, followed by acetylation and Baeyer-Villiger oxidation of the resulting -acetoxyketone (−)-14 afforded (−)-5-O-acetyl-2-O-benzyl-3-deoxy-β-D-arabino-hexofuranurono-6,1-lactone ((−)-15). This compound was converted readily into (+)-methyl 3-deoxy--D-arabino-hexofuranoside ((+)-6 and (+)-methyl 3-deoxy-β-L-xylo-hexofuranoside ((+)-7) and partially protected derivatives. (−)-15 was also converted into 4-deoxy-D-lyxo-hexopyranose (34) and several partially protected derivatives such as (+)-methyl 4-deoxy-2,3-O-isopropylidene--D-lyxo-hexopyranoside ((+)-8).     

Synthesis of chiral 2-furyl and 3-nitro-7-oxabicyclo[2.2.1]heptane derivatives from sugars

Asymmetric Diels–Alder reactions between 2-methylfuran and chiral (E)-1,2-dideoxy-1-nitroalkenes derived from d-mannose and d-galactose were carried out at room temperature, under 13 kbar pressure. The processes were completely regioselective, and only the four adducts with penta-O-acetyl-1′-C-(4-methyl-3-nitro-7-oxabicyclo[2.2.1]hept-5-en-2-yl)pentitols structures were formed in each case. These adducts, as well as those arising from cycloadditions of the same nitroalkenes and furan, have been converted into chiral derivatives, such as 2-furyl substituted 1-nitrosugars, 2-glyco-4-methyl-3-nitro-7-oxabicyclo[2.2.1]heptanes, and 5,6-exo-epoxy-2-glyco-3-nitro-7-oxabicyclo[2.2.1]hept-5-enes.     

Total synthesis of (±)-methyl 3-(3-isocyano-6-oxabicyclo[3.1.0]hex-2-en-5-yl)-2-propenoate

The total synthesis of (±)-methyl 3-(3-isocyano-6-oxabilcyclo[3.1.0]hex-2-en-5-yl)-2-propenoate has been achieved using 3-tosyl-2-azabicyclo[2.2.1]hepta-2,5-diene as a key starting material.     

Derivatives of 7-Oxabicyclo[2.2.1 ]hept-5-ene and 7-Oxabicyclo[2.2.1 ] heptane. Synthesis,transformations, and stereochemistry using nmr methods

Synthesis and stereochemistry of various endo-2- and exo-2-substituted-7-oxabicyclo[2.2.1]-hept-5-enes and -heptanes are described. The nmr spectra of several derivatives are reported and discussed. Use is made of this data to allow determination of the stereochemical integrity of the system. Facile chromatographic separation methods were found for endo- and exo-2-sub-stituted-7-oxabicyclo[2.2.1 ]hept-5-enes and -heptanes.     

Asymmetric Synthesis and DNA Intercalation of (-)-6-[[(Aminoalkyl)oxy]methyl]-4-demethoxy-6,7- dideoxydaunomycinones(1)(,)

The BF(3).Et(2)O-promoted Diels-Alder addition of 1-acetylvinyl RADO(Et)-ate (RADO(Et)-ate = 3-ethyl-2-oxo-6,8-dioxa-3-azabicyclo[3.2.1]octane-7-exo-carboxylate) to 1-(dimethoxymethyl)-2,3,5,6-tetramethylidene-7-oxabicyclo[2.2.1]heptane led to one major monoadduct that added to 1,2-didehydrobenzene and was converted into (-)-4-demethoxy-7-deoxydaunomycinone and (2R)-12-acetoxy-2-acetyl-5-(bromomethyl)-1,2,3,4-tetrahydronaphthacen-2-yl RADO(Et)-ate. The latter compound was used to construct (8R)-8-acetyl-6,8-dihydroxy-11-[[(3'-[(aminopropyl)oxy]-, -4'-[(aminobutyl)oxy], and -5'-[(aminopentyl)oxy]methyl]-7,8,9,10-tetrahydronaphthacene-5,12-dione hydrochloride (-)-8, (-)-9, (-)-10, respectively, as well as (8R)-8-acetyl-6,8-dihydroxy-11- [[[2'-[(3"-aminopropyl)amino]ethyl]oxy]- ((-)-11) and -[[3'-[(3"-aminopropyl)amino]propyl]oxy]methyl]-7,8,9, 10-tetrahydronaphthacene-5,12-dione hydrochloride ((-)-12). (8R)-8-Acetyl-6,8-dihydroxy-11-[[(alpha-L-daunosaminyl)oxy]methyl]-7,8,9,10-tetrahydronaphthacene-5,12-dione hydrochloride ((-)-13), a mimic of idarubicin, was also prepared. Absorbance and fluorescence titration experiments showed (-)-8, (-)-9, and (-)-10 to intercalate calf thymus DNA whereas (-)-11, (-)-12, and (-)-13 did not. The best intercalator was (-)-9 (K(b) = (1.1 +/- 0.1) x 10(5) M(-)(1)) with the [(4'-aminobutyl)oxy]methyl chain. Inhibition of topoisomerase II-induced DNA strand religation was observed for (-)-8 at a concentration of 50 &mgr;M.     

Synthesis and Stereostructure of 3-Amino-5- and -6-hydroxybicyclo[2.2.1]heptane-2-carboxylic Acid Diastereomers

Summary. All-endo-3-amino-5-hydroxybicyclo[2.2.1]heptane-2-carboxylic acid and two epimers of 3-amino-6-hydroxybicyclo[2.2.1]heptane-2-carboxylic acid were prepared via 1,3-oxazine or γ-lactone intermediates by the stereoselective functionalization of endo-3-aminobicyclo[2.2.1]hept-5-ene-2-carboxylic acid derivatives. Their structures were proved by IR and NMR spectroscopy, with the use of HMQC, HMBC, DEPT, and DIFFNOE techniques.     

Synthesis and Stereostructure of 3-Amino-5- and -6-hydroxybicyclo[2.2.1]heptane-2-carboxylic Acid Diastereomers

All-endo-3-amino-5-hydroxybicyclo[2.2.1]heptane-2-carboxylic acid and two epimers of 3-amino-6-hydroxybicyclo[2.2.1]heptane-2-carboxylic acid were prepared via 1,3-oxazine or γ-lactone intermediates by the stereoselective functionalization of endo-3-aminobicyclo[2.2.1]hept-5-ene-2-carboxylic acid derivatives. Their structures were proved by IR and NMR spectroscopy, with the use of HMQC, HMBC, DEPT, and DIFFNOE techniques.