Peculiarities of electroreduction of trans-2-allyl-6-methyl(allyl,phenyl)-1,2,3,6-tetrahydropyridines

Electrochemical reduction of trans-2-allyl-6-R-1,2,3,6-tetrahydropyridines (R = Me, All, and Ph) on the mercury cathode in anhydrous DMF (with 0.1 M Bu₄NClO₄ as the supporting electrolyte) resulted in catalytic hydrogen evolution, while in the case of anhydrous DMF the electrochemical activity of the endocyclic double bond was dictated by the nature of the R substituent at the carbon atom neighboring the double bond. The electrocatalytic hydrogenation of the piperideines under study on the Ni (Ni_disp/Ni) cathode in 40% aqueous DMF in the presence of a tenfold excess of AcOH yielded the corresponding trans-2-propyl-6-R¹-piperidines (R¹ = Me, Pr, and Ph). Using trans-2,6-diallyl-1,2,3,6-tetrahydropyridine as an example, the conditions (with annealed copper as the cathode) for selective hydrogenation of the double bonds in allyl substituents with preservation of the endocyclic double bond were found.     

Dynamic 1H NMR Study of Aryl-Nitrogen Single Bond and Carbon-Carbon Double Bond Rotational Energy Barriers in Two Highly Functionalized Pyranopyrimidines

 The reactive 1:1 intermediate produced in the reaction between 2,6-dimethylphenyl isocyanide and dimethyl acetylenedicarboxylate was trapped by N,N′ -dimethylbarbituric acid to yield the isomeric products dimethyl 7-(2,6-dimethylphenylamino)-1,3-dimethyl-2,4-dioxo-4H-pyrano[3,2-d]pyrimidine-5,6-dicarboxylate and dimethyl (E)-2-((2,6-dimethylphenylamino)-(1,3-dimethyl-2,4,6-trioxo-pyrimidine-5-ylidene)-methyl)-but-2-enedioate in a nearly 1:1 ratio and an overall yield of 85%. Dynamic effects were observed in the ¹H NMR spectra of these compounds and were attributed to restricted rotation around the aryl-nitrogen single bonds and the polarized carbon-carbon double bond.     

Synthesis of 5′-azido- and 5′-amino-2′,5′-dideoxynucleosides from quinazoline-2,4(1H,3H)-diones

Quinazoline-2,4(1H,3H)-diones 4 were silylated and condensed with methyl 5-azido-2,5-dideoxy-3-O-(4-methylbenzoyl)-α,β-D-erythro-pentofuranoside (3) using trimethylsilyl trifluoromethanesulfonate (TMS triflate) as the catalyst to afford the corresponding 5′-azidonucleosides 5 . 1-(5-Azido-2,5-dideoxy-α-D-erythro-pentofuranosyl)quinazoline-2,4(1H,3H)-diones 6 and the corresponding β anomers were obtained by treating 5 with sodium methoxide in methanol at room temperature. 6-Methyl-1-(5-amino-2,5-dideoxy-β-D-erythro-pentofuranosyl)quinazoline-2,4(1H,3H)-dione (8) was obtained by treatment of the corresponding azido derivative 7 with triphenylphosphine in pyridine, followed by hydrolysis with ammonium hydroxide.     

Carbon-13 nuclear magnetic resonance spectra of N-substituted 2-amino-4H-3,1-benzoxazin-4-ones and 3-substituted 2,4-(1H,3H)quinazolinediones

¹³C chemical shifts of nine N-substituted 2-amino-4H-3,1-benzoxazin-4-ones, the isomeric 3-substituted 2,4-(1H,3H)quinazolinediones, and the parent compounds of the two series are reported. Support is provided for the endocyclic position of the C=N bond in the former series of compounds.     

Dynamic 1H NMR Study of Aryl-Nitrogen Single Bond and Carbon-Carbon Double Bond Rotational Energy Barriers in Two Highly Functionalized Pyranopyrimidines

Summary.  The reactive 1:1 intermediate produced in the reaction between 2,6-dimethylphenyl isocyanide and dimethyl acetylenedicarboxylate was trapped by N,N′ -dimethylbarbituric acid to yield the isomeric products dimethyl 7-(2,6-dimethylphenylamino)-1,3-dimethyl-2,4-dioxo-4H-pyrano[3,2-d]pyrimidine-5,6-dicarboxylate and dimethyl (E)-2-((2,6-dimethylphenylamino)-(1,3-dimethyl-2,4,6-trioxo-pyrimidine-5-ylidene)-methyl)-but-2-enedioate in a nearly 1:1 ratio and an overall yield of 85%. Dynamic effects were observed in the ¹H NMR spectra of these compounds and were attributed to restricted rotation around the aryl-nitrogen single bonds and the polarized carbon-carbon double bond. Received September 18, 2000. Accepted (revised) November 22, 2000     

Thiazoles and thiadiazines. The condensation of ethyl 4-chloroacetoacetate with thiosemicarbazide

By varying the acidity, solvent polarity, and temperature when thiosemicarbazide reacted with ethyl 4-chloroacetoacetate, ethyl 2-amino-6H-1,3,4-thiadiazine-5-acetate hydrochloride, ethyl 2-hydrazinothiazole-4-acetate, and ethyl 2-imino-3-aminothiazoline-4-acetate hydrochloride were prepared selectively. Double bond migration occurred after neutralizing the thiadiazine and thiazoline hydrochlorides to form the α,β-unsaturated esters: 2-amino-5-carbethoxymethylidene-4,5-dihydro-6H-1,3,4-thiadiazine and 2-imino-3-amino-4-carbethoxymethylidenethiazolidine. Pmr studies revealed that an equilibrium existed in solution between the imine and enamine tautomers of the thiadiazine free base. In the enamine structure, a 6-membered hydrogen bonded ring system promotes stability. The thiadiazine contracted in acidic aqueous acetone to ethyl 2-isopropylidenehydrazonothiazole-4-acetate. Monobenzoylation at the primary amine of the thiadiazine yielded ethyl 2-benzamido-6H-1,3,4-thiadiazine-5-acetate without disruption of the hydrogen bonded ring, but benzoylating the imino functionality of the thiazolidine caused deconjugation of the α,β-unsaturated ester by double bond migration back into the ring, and ethyl 2-benzimido-3-aminothiazoline-4-acetate was produced, dehydration yielded ethyl 2-phenylthiazolo[3,2-b]-s-triazole-5-acetate. This compound was also obtained by reacting 3-phenyl-1,2,4-triazole-5-thiol with ethyl 4-chloroacetoacetate, while the monobenzoylated derivative of the hydrazinothiazole, ethyl 2-(2-benzoylhydrazino)thiazole-4-acetate underwent a dehydrative cyclization to ethyl 3-phenyl-thiazolo [2,3-c]-s-triazole-5-acetate. In chloroform solvent, the second site of benzoylation on the thiadiazine was ring nitrogen 3 while in ethanol or acetonitrile-pyridine ring nitrogen 4 was benzoylated instead. Benzoylation at ring nitrogen 3 resulted in deconjugation of the α,β-unsaturated ester moiety and formed the endocyclic imine, ethyl 2-benzimido-3-benzoyl-2,3-dihydro-6H-1,3,4-thiadiazine-5-acetate. However, deconjugation of the unsaturated ester did not occur after benzoylation at ring nitrogen 4; the product was trans-2-benzamido-4-benzoyl-5-carbethoxymethylidene-4,5-dihydro-6H-1,3,4-thiadiazine. The hydrogen bonded oximes, syn-2-amino-5-ethyloxalyl-6H-1,3,4-thiadiazine oxime, 3,3-dimethyl-5-ethyloxalyl-2H-1,2,4-triazolo[3,4-b]thiazole oxime, and 2-(2-benzoylhydrazino)-4-ethyloxalylthiazole oxime were synthesized by nitrosation. 2-Amino-5-ethyloxalyl-6H-1,3,4-thiadiazine oxime benzoate, 2-benzamido-5-ethyloxalyl-6H-1,3,4-thiadiazine oxime dibenzoate, and the tribenzoylated derivatives, 2-benzimido-3-benzoyl-5-ethyloxalyl-2,3-dihydro-6H-1,3,4-thiadiazine oxime benzoate and 2-benzamido-4-benzoyl-5-ethyl-oxalyl-4H-1,3,4-thiadiazine oxime benzoate, of the thiadiazine oxime werè prepared. The oxime benzoylated first, the primary amine second, and the number 3 and 4 ring nitrogens last.     

β-Eliminativer Abbau bei 4-0-substituierten Hexopyranosiduronat-Derivaten

Two types of endocyclic enol-acetal forming β-elimination were investigated on synthetic model compounds. In both types the 4-O-methanesulfonyl residue was chosen as leaving group. The a,e-β-elimination was proved on 2,3-benzyl ether protected D -glucopyranosiduronate derivatives I, and the a, a-β-elimination on the analogous substituted D -galactopyranosiduronates XVII. Using a small excess of KOH in methanol at 25°, a quick elimination of a molecule of methanesulfonic acid was observed, and as reaction product the 4,5-unsaturated 4-deoxyhexopyranosiduronate derivative II was obtained. Only an unimportant stereoselectivity was found between the a,e- and a,a-mesylate β-eliminations. The 4,5-unsaturated 4-deoxyhexopyranosiduronates show a strong UV. maximum at 238 nm, and Cotton effects in the ORD. spectra. This stable ring system with an endocyclic enol-acetal linkage is present in a half-chair (H) conformation. The structure of the unsaturated deoxyhexopyranosiduronate obtained was established by structure- and stereo-correlation with a 2-deoxy-L -xylose derivative, showing that a ring contraction during the β-elimination does not occur.     

Recherches sur la formation et la transformation des esters LXXII. Aryl(ou aralcoyl ou alcoyl)amino-2-tétrahydro-m-thiazines ou aryl(ou aralcoyl ou alcoyl)amino-2-dihydro-Δ2-m-thiazines et dérivés

3-Aminopropanol reacts with aryl(or aralkyl or alkyl)isothiocyanates R? N?C?S to yield the corresponding thio-ureas R? NH? CS? NH? (CH₂)₃OH which, refluxed with hydrochloric acid, are cyclized by elimination of water. The cyclization products are identical with the hydrothiazines resulting by elimination of sulfate or phosphate from the sulfuric or phosphoric monoesters of these thio-ureas. The resulting hydrothiazines are either 2-(R-imino)-tetrahydro-m-thiazines (I) or 2-(R-amino)-dihydro-Δ²-m-thiazines (II). Their structure has been established by comparison of their spectra with those of model compounds in one of which the C?N double bond is certainly endocyclic (2-methyl-dihydro-Δ²-m-thiazine), the other presenting an exocyclic C?N double bond (3-methyl-2-phenylimino-tetrahydro-m-thiazine). When R is an aryl group, the C?N double bond is exocyclic (structure I with >C?N? Ar), and one may presume that this structure is stabilized by resonance. When R is an aralkyl or an alkyl group, the C?N double bond is endocyclic (structure II). The nmr spectra were taken with three types of solvent: CDCl₃ or CCl₄; (CD₃)₂SO; CF₃COOH. In CF₃COOH solution the benzylic protons of the hydrothiazine with R = pF? C₆H₄CH₂? couple with NH (J=5,5cps) which confirms the endocyclic position of the C?N double bond in this case.     

Stereochemical effects in the nitrosation of some α,β-unsaturated ketoximes. Formation of 1-hydroxypyrazole 2-oxides and 4-oximino-4,5-dihydroisoxazoles

Several α,β-unsaturated ketoximes R¹CH=CHC(=NOH)R² were nitrosated using butyl nitrite in aqueous ethanol in the presence of copper(II) sulfate and pyridine. The product distribution varied depending on whether the oxime hydroxyl group was syn or anti with respect to the carbon?carbon double bond. The anti-oximes gave the copper complexes of 1-hydroxypyrazole 2-oxides in high yields. The isomeric syn-oximes gave lower yields of the pyrazole complexes along with 4-oximino-4,5-dihydroisoxazole derivatives. For the syn-oximes where R¹ is phenyl and R² is either methyl or ethyl, conversion of the oximes to the parent ketones was also observed. The results may be explained by processes involving N-nitrosonitrone intermediates.     

Synthesis of Heterocyclic‐Substituted Novel Hydroxysteroids with Regioselective and Stereoselective Reactions

Polyhydroxy steroids bearing the 3β,5α,6β‐trihydroxy pattern were synthesized from different heterocyclic‐substituted unsaturated steroid by an easy and simple method with high yields. The endocyclic double bond of thiophene‐substituted and quinoline‐substituted steroids were converted to the trans‐diaxial diol by the regioselective and stereoselective reactions with m‐chloroperoxybenzoic acid in the basic medium.     

Réactions de Friedel et Crafts de dérivés aromatiques sur les composés dioxo-1,4,2,3-non saturés. IV. Réactions des hydroxy-5-ouchloro-5-diméthyl-3,5- ou diméthyl-4,5-dihydro-2,5-furannones-2

Friedel-Crafts reactions of aromatic derivatives with 1,4-dicarbonyls 2,3-éthylenic compounds. Part IV. Reactions of 5-hydroxy or 5-chloro 3,5-dimethyl or 4,5-dimethyl 2 (5 H) furanones We studied the Friedel-Crafts reactions of 2-(5H)-furanones. In the presence of sulfuric acid and of an aromatic derivative, 5-hydroxy- or 5-chloro-5-methyl-2-(5H)-furanones with one methyl group either in the 3 position, or in the 4 position generally give the corresponding 5-aryl-2-(5H)-furanones, while with aluminium chloride, it is possible to obtain, when a reaction takes place, isomeric 1H-indenecarboxylic acids. However, in a particular case, an addition to the substrate's double bond is observed. The 3-aryl-5-hydroxy-tetrahydrofuran-2-one obtained is methylated in two ways and gives either a cyclic product, or a linear one. In two cases tautomerism between 1H-1-indenecarboxylic acid and 1H-3-indenecarboxylic has been shown by ¹H-NMR.     

Synthesis of polycyclic cyclopropanecarboxylic acids and their esters based on catalytic cyclopropanation of 6,6-dimethylfulvene

Reactions of 6,6-dimethylfulvene with methyl diazoacetate in the presence of Cu compounds is accompanied by methoxycarbonylmethylenation of the endocyclic double bonds to give the corresponding mono- and diadducts in total yields of up to 85% with marked predominance ofanti-isomers. The subsequent cyclopropanation of monoadducts with diazomethane in the presence of Pd compounds also involves the endocyclic double bond and gives esters of tricyclo[4.1.0.0.^2,4]heptanecarboxylic acid in high yields. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 528–531, March, 1997.     

The Non-planarity of the Bicyclo[2.2.1]hept-2-ene Double bond. Crystal Structures of Bicyclo[2.2.2]oct-2-ene,Bicyclo[2.2.1]hept-2-ene,and Bicyclo[2.1.1]hex-2-ene Systems

The crystal structures of (1R,4R,5S,8S)-9,10-dimethylidentricyclo[6.2.1.0^2,7]undec2(7)-ene-4,5-dicarboxylic anhydride ( 3 ), (1R,4R,5S,8S)11-isopropylidene-9,10-dimethylidenetricyclo[6.2.1.m^2,7]undec-2(7)-ene-4,5-dicarboxylic anhydride ( 6 ), (1R,4R,5S8S)-9,10-dimethylidenetricyclo[6.2.2.0^2,7]dodec-2(7)-ene-4,5-dicarboxylic anhydride ( 9 ), (1R4R5S8S)-TRICYCLO[6.2.2.0^2,7]dodeca-2(7), 9-diene-4,5-dicarboxylic anhydride ( 12 ) and (4R,5S)-tricyclo[6.1.1.0^2.7]dec-2(7)-ene-4,5-dicarboxylic acid ( 16 ) were established by X-ray diffraction. The alkyl substituents onto the endocyclic bicyclo[2.2.1]hept-2-ene double bond deviate from the C(1), C(2), C(3), C(4), plane by 13.5°4 in 3 and by 13.9° in 6 , leaning toward the endo-face. No such out-of-plane deformations were observed with the bicyclo[2.2.2]oct-2-ene derivatives 9 and 12 . The exocyclic s-cis-butadiene moieties in 3, 6 and 9 do not deviate significantly from planarity. The deviation from planarity of the double bond n bicyclo[2.2.1]hept-2-ene derivatives and planarity in bicyclo[2.2.2]oct-2-ene analogues is shown to be general by analysis of all known structures in the Cambridge Crystallographic Data File. The non-planarity of the bicyclo[2.2.1]hept-2-ene double bond cannot be attributed only to bond-angle deformations which would favour rehybridizatoin of the olefinic C-atoms since the double bond in the more strained bicyclo[2.1.1]hex-2-ene drivative 16 deviates from planarity by less than 4°.     

Valenzisomerisierung von cis-Dienonen,II. 5-Phenylpenta-2, 4-dienaldehyde [1]

The 5-Phenylpenta-2,4-dienaldehydes 4 , and 7 , show an uncatalized cis-trans-isomerization of the 4,5-double bond above 70 °C. The negative value of the activation entropy for these reactions points to the formation of the bicyclic valence isomeric 2H-Pyrans 5 and 8 respectively in the rate determining step. Intermediate 5 can be trapped as its tetracyanoethylene cycloadduct 11 . The cis-trans isomeric 1,6-diphenyl-hexa-1,3,5-trienes 12a and 12b undergo above 150° a disrotatory ring closure to the bicyclic dienes 13 and 14 respectively.     

Palladium-catalyzed conjugate addition type reaction of 5-iodopyrimidines with α,β-unsaturated ketones

The reaction of various 5-iodopyrimidines with α,β-unsaturated ketones in the presence of palladium diacetate-triphenylphosphine complex in triethylamine are investigated. In the reaction of 2,4-dialkoxy(or alkylthio)-6-methyl-5-iodopyrimidine the addition of pyrimidine to the carbon? carbon double bond of α,β-unsaturated ketones occurs. In the case of other pyrimidines, according to the decrease of steric hindrance at the 5-position on the pyrimidine ring, the ratio of conjugate addition product was decreased and the usual olefinic substituted product was increased.     

Synthesis of 2,6-Dideoxy-6-Thio Derivatives of KDO

ABSTRACT

Ammonium 2,3,6-trideoxy-2,6-epithio-D-manno-2-octenoate (8), ammonium 2,3,6-trideoxy-2,6-epithio-D-glycero-D-talo-octanoate (10a), ammonium 2,3,6-trideoxy-2,6-epithio-D-glycero-D-galacto-octanoate (10b) and ammonium 2,3,6-trideoxy-2,6-epithio-oxa-D-glycero-D-galacto-octanoate (13) have been synthesised as potential inhibitors of the enzyme CMP-KDO synthetase. The key step in the synthesis of 8 was the elimination of water from methyl 3,6-dideoxy-4,5:7,8-di-O-isopropylidene-6-thio-D-manno-2-octulosonate (4) using chlorodiphenylphosphine, imidazole and bromine to give the unsaturated methyl 2,3,6-trideoxy-2,6-epithio-4,5:7,8-di-O-isopropylidene-D-manno-2-octenoate (5). For the synthesis of 10a and 10b, zinc reduction of methyl 3,6-dideoxy-4,5:7,8-di-O-isopropylidene-6-S-(4-methoxybenzyl)-6-thio-2-O-(trichloro-tert-butoxycarbonyl)-D-manno-2-octenoate (2) gave an epimeric mixture of an α-hydroxyester 6 which was ring closed by in situ activation of the hydroxyl group using triphenylphosphine and tri-iodoimidazole followed by cleavage of the p-methoxybenzyl group to give 7a and 7b, which then were deprotected to give 10a and 10b.     

Treatment of diazoalkanes with unsaturated compounds. No. 5. Catalytic cyclopropanation of unsaturated hydrocarbons with diazoethane

Conclusions The preparative catalytic cyclopropanation of unsaturated hydrocarbons with diazoethane has been achieved for the first time. Addition of the ethylidene fragment to the C=C double bond occurs in a nonstereoselective manner and leads to the formation of the corresponding methylcyclopropanes in 55–70% total yields. In the presence of CuCl, all double bonds of unsaturated hydrocarbons are cyclopropanated with equal facility, whereas in the presence of (PhCN)₂PdCl₂, preferential regioselective cyclopropanation of strained endocyclic and terminal double bonds is observed, just as was true in the case of reactions with diazomethane.For Communication No. 4, see [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1338–1343, June, 1987.     

Acyl iodides in organic synthesis. Reactions with morpholine,piperidine, and <Emphasis Type="Italic">N</Emphasis>-hydrocarbylpiperidines

Acyl iodides RCOI (R = Me, Ph) reacted with morpholine and piperidine to give the corresponding N-acyl derivatives and morpholine or piperidine hydroiodides. Reactions of acyl iodides with N-methyl- and N-ethylpiperidines involved cleavage of the exocyclic R-N bond with formation of N-acylpiperidine and alkyl iodide and were accompanied (to insignificant extent) by cleavage of the endocyclic N-C bond, leading to N-alkyl-N-(5-iodopentyl)acylamides. In the reaction of acetyl iodide with N-phenylpiperidine, the main process was cleavage of just endocyclic N-C bond to produce N-(5-iodopentyl)-N-phenylacetamide and its dehydroiodination product, N-(pent-4-en-1-yl)-N-phenylacetamide. Analogous reaction with benzoyl iodide afforded N-(5-iodopentyl)-N-phenylbenzamide in a poor yield.     

Isolation and Structural Study on Carbohydrates from Cynanchum otophyllum and Cynanchum paniculatum

Three new carbohydrates were isolated from the acidic hydrolysis part of the ethyl acetate extract of Cynanchum otophyllum Schneid (Asclepiadaceae) and one new carbohydrate from the ethyl acetate extract of Cynanchum paniculatum Kitagawa. Their structures were determined as methyl 2,6-dideoxy-3-O-methyl-α-D-arabino-hexopyranosyl-(1 → 4)-2,6-deoxy-3-O-methyl-β-D-arabino-hexopyranosyl-(1 → 4)-2,6-dideoxy-3-O-methyl-α-D-arabino-hexopyranoside (1), ethyl 2,6-dideoxy-3-O-methyl-β-D-ribo-hexopyranosyl-(1 → 4)-2,6-dideoxy-3-O-methyl-α-l-lyxo-hexopyranoside (2), met hyl 2,6-dideoxy-3-O-methyl-α-l-ribo-hexopyranosyl-(1 → 4)-2,6-dideoxy-3-O-methyl-β-D-lyxo-hexopyranosyl-(1 → 4)-2,6-dideoxy-3-O-methyl-α-D-arabino-hexopyranoside (3), and 2,6-dideoxy-3-O-methyl-β-D-ribo-hexopyranosyl-(1 → 4)-2,6-dideoxy-3-O-methyl-α-d-arabino-hexopyranosyl-(1 → 4)-2,6-dideoxy-3-O-methyl-α -d-arabino-hexopyranose (4), respectively, by spectral methods.     

Enzyme‐Mediated Preparation of (+)‐ and (−)‐β‐Irone and (+)‐ and (−)‐cis‐γ‐Irone from Irone alpha®

The (−)‐ and (+)‐β‐irones ((−)‐ and (+)‐ 2 , resp.), contaminated with ca. 7 – 9% of the (+)‐ and (−)‐trans‐α‐isomer, respectively, were obtained from racemic α‐irone via the 2,6‐trans‐epoxide (±)‐ 4 (Scheme 2). Relevant steps in the sequence were the LiAlH₄ reduction of the latter, to provide the diastereoisomeric‐4,5‐dihydro‐5‐hydroxy‐trans‐α‐irols (±)‐ 6 and (±)‐ 7 , resolved into the enantiomers by lipase‐PS‐mediated acetylation with vinyl acetate. The enantiomerically pure allylic acetate esters (+)‐ and (−)‐ 8 and (+)‐ and (−)‐ 9 , upon treatment with POCl₃/pyridine, were converted to the β‐irol acetate derivatives (+)‐ and (−)‐ 10 , and (+)‐ and (−)‐ 11 , respectively, eventually providing the desired ketones (+)‐ and (−)‐ 2 by base hydrolysis and MnO₂ oxidation. The 2,6‐cis‐epoxide (±)‐ 5 provided the 4,5‐dihydro‐4‐hydroxy‐cis‐α‐irols (±)‐ 13 and (±)‐ 14 in a 3 : 1 mixture with the isomeric 5‐hydroxy derivatives (±)‐ 15 and (±)‐ 16 on hydride treatment (Scheme 1). The POCl₃/pyridine treatment of the enantiomerically pure allylic acetate esters, obtained by enzymic resolution of (±)‐ 13 and (±)‐ 14 , provided enantiomerically pure cis‐α‐irol acetate esters, from which ketones (+)‐ and (−)‐ 22 were prepared (Scheme 4). The same materials were obtained from the (9S) alcohols (+)‐ 13 and (−)‐ 14 , treated first with MnO₂, then with POCl₃/pyridine (Scheme 4). Conversely, the dehydration with POCl₃/pyridine of the enantiomerically pure 2,6‐cis‐5‐hydroxy derivatives obtained from (±)‐ 15 and (±)‐ 16 gave rise to a mixture in which the γ‐irol acetates 25a and 25b and 26a and 26b prevailed over the α‐ and β‐isomers (Scheme 5). The (+)‐ and (−)‐cis‐γ‐irones ((+)‐ and (−)‐ 3 , resp.) were obtained from the latter mixture by a sequence involving as the key step the photochemical isomerization of the α‐double bond to the γ‐double bond. External panel olfactory evaluation assigned to (+)‐β‐irone ((+)‐ 2 ) and to (−)‐cis‐γ‐irone ((−)‐ 3 ) the strongest character and the possibility to be used as dry‐down note.