Synthesis of naturally occurring diene and trienes by Te/Li exchange on (1Z,3Z)-butyltelluro-4-methoxy-1,3-butadiene

(1Z,3Z)-Butyltelluro-4-methoxy-1,3-butadiene 2 was obtained by the hydrotelluration of (Z)-1-methoxy-but-1-en-3-ynes 1. The butadienyllithium 3 obtained by the Te/Li exchange reaction in the (1Z,3Z)-1-butyltelluro-4-methoxy-1,3-butadiene 2 reacted with aldehydes to form the corresponding alcohols 4a-d with total retention of configuration. The alcohols formed undergo hydrolysis, resulting in the α,β,γ,δ-unsaturated aldehydes of (E,E) configuration, which are precursors of trienes obtained from natural sources. The products of this reaction were employed in the synthesis of methyl-(2E,4E)-decadienoate 7, which is a component of the flavor principles of ripe Bartlett pears. Performing the Wittig reaction of the methyl triphenylphosphorane with the deca-(2E,4E)-dienal 5a, we were able to synthesize the undeca-(1,3E,5E)-triene 6a. This compound is a sex-pheromone component of the marine brown algae Fucus serratus, Dictyopteris plagiograma, and Dictyopteris australis. Performing the Wittig reaction of methyl triphenylphosphorane with the octa-(2E,4E)-dienal 5c, the nona-(1,3E,5E)-triene 6b was synthesized. The compound obtained is a sex-pheromone component of the marine brown alga Sargassum horneri. The octa-(1,3E,5E)-triene 6c was easily obtained from hepta-(2E,4E)-dienal 5d by the Wittig reaction with methyl triphenylphophorane. This compound is a sex-pheromone component of the marine brown alga Fucus serratus.     

Novel (E)- and (Z)-3(5)-(2-hydroxyphenyl)-4-styrylpyrazoles from (E)- and (Z)-3-styrylchromones: the unexpected case of (E)-3(5)-(2-hydroxyphenyl)-4-(4-nitrostyryl)pyrazoles

An efficient synthetic method for the preparation of (E)- and (Z)-3(5)-(2-hydroxyphenyl)-4-styrylpyrazoles has been developed. The reaction of (E)- and (Z)-3-styrylchromones with hydrazine hydrate afforded the corresponding (E)- and (Z)-4-styrylpyrazoles, respectively, saved 4′-nitro-derivatives where both (E)- and (Z)-4′-nitro-3-styrylchromones afforded (E)-3(5)-(2-hydroxyphenyl)-4-(4-nitrostyryl)pyrazoles. The reaction mechanism for these transformations was discussed and the stereochemistry of all products was assigned by NMR experiments.     

Vinyltetrazoles: III. Metal-catalyzed arylation, a new method of vinyltetrazoles functionalization

New functionalization procedure was developed for C- and N-vinyltetrazoles based on Heck reaction. Applying this method diverse (E)-styryl- and (E)-distyryltetrazoles were obtained for the first time in 76?C85% yields. C-Vinyltetrazoles are more reactive in Heck cross-coupling than N-vinyltetrazoles. The arylation of 1-vinyltetrazole along Heck reaction proceeds with a C-H-activation and leads to the formation of 5-phenyl-1-[2-(E)-phenylethenyl]tetrazole.     

A convergent and stereoselective synthesis of a seco-precursor of macrolactin A

A seco-precursor of macrolactin A was synthesized by coupling two advanced segments. Wittig reaction and Horner-Emmons reaction were utilized to construct the three characteristic E,Z and E,E dienes. The C₁-C₁₀ segment was synthesized through Horner-Emmons reaction with phosphonate reagent. The α-alkylation of sulfone stabilized anion with allyl bromide followed by desulfonation gave the C₁₁-C₂₄ segment.     

Synthesis of eleven-membered carbocycles via a homo-Cope type of five-carbon ring expansion reaction utilized β-(hydroxymethyl)allylsilane

Eleven-membered carbocycles were synthesized from six-membered compounds fitted with a β-(hydroxymethyl)allylsilane unit via the title reaction. Namely, trans- and cis-(E)-2-(trimethylsilylmethyl)-3-(2-vinylcyclohex-1-yl)prop-2-en-1-ol were treated with Tf₂O in CH₂Cl₂ in the presence of 2,6-lutidine to afford (1E)-3-methylenecycloundeca-1,6-diene in good yield. The geometry of the product was shown to depend upon the trans- and cis-substitution pattern on the cyclohexane ring of the substrates; i.e. trans-isomer afforded (6E)-product exclusively and cis-isomer afforded the mixture of (6E)- and (6Z)-product in 1:2 ratio. The (Z)-substrate with respect to allylsilane moiety afforded the same ring expansion product, however, the yield was lower than the reaction with the (E)-substrate. The substrates bearing t-butyl or benzyloxy substituents on the cyclohexane ring also afforded the product analogously, indicating that the reaction depends upon the conformation of the substrate. On the other hand, the substrate bearing isopropenyl group instead of a simple vinyl group did not afford the ring expansion product but produced bicyclo[5.4.0]undecane via the ene reaction.     

Asymmetric total synthesis of (+)-carneic acid A and structure revision of its natural form

This Letter describes the asymmetric total synthesis of (+)-carneic acid A via the stereoselective IMDA reaction of (E,E,E)-triene, which was prepared from the commercially available methyl (S)-3-hydroxy-2-methylpropionate. By this asymmetric total synthesis, we verified that the reported absolute structure of naturally occurring carneic acid A must be revised.     

A DSC study on the kinetics of disproportionation reaction of (hfac)Cu(COD)

The kinetics of disproportionation reaction of hexafluoroacetylacetonate-copper(I)-cycloocta-1,5-diene [(hfac)Cu^I(COD)] was investigated by the use of differential scanning calorimetry (DSC) with different heating rates in dynamic nitrogen atmosphere. First, the activation energies (E_as) of the disproportionation reaction were estimated with model-free isoconversional methods, respectively. The E_as were found to fall within the range between 17.6 and 18.7 kJ mol⁻¹, with no temperature and heating rate effects observed. Then, when the E_a was ascertained, the model-fitting methods with least square fitting procedure were adopted to determine the kinetic model for the disproportionation reaction. As a result, the disproportionation reaction follows second-order reaction kinetics.     

Domino pericyclic reactions of acyclic conjugated (E,Z,E,E)-tetraenes

Acyclic conjugated (E,Z,E,E)-tetraenes, upon thermolysis, undergo a domino pericyclic process involving 6π electrocyclisation of the (E,Z,E)-triene moiety to give the corresponding cis-disubstituted 5-vinyl-1,3-cyclohexadienes, followed by an intramolecular Diels-Alder reaction with the vinyl side chain to give tricyclo[3.2.1.0^2,7]oct-3-enes.     

Stereoselective synthesis of 4-fluoro-1,3-alkadienylboronates and their application in the stereoselective synthesis of fluoropolyenes

(1E,3E)- and (1E,3Z)-4-fluoro-1,3-alkadienylboronates were stereoselectively prepared by the Heck-reaction of a vinylboronate with (E)- or (Z)-2-fluoro-1-alkenyliodonium salts, and applied to the Suzuki-Miyaura coupling reaction for the synthesis of fluoropolyenes.     

The stereoselective synthesis of (E)-octafluoro-1,3,5-hexatriene and (3E,5E,7E)-dodecafluoro-1,3,5,7,9-decapentaene

(E)-(1,2-Difluoro-1,2-ethenediyl)bis[tributylstannane], 3, readily undergoes a Pd(PPh₃)₄/CuI-catalyzed cross-coupling reaction with iodotrifluoroethene to yield (E)-octafluoro-1,3,5-hexatriene, 4, in high isomeric purity. (1Z,3E,5Z)-(1,2,3,4,5,6-Hexafluoro-1,3,5-hexenetriyl)bis[tributylstannane], 7, was sequentially prepared from (1Z,3E,5Z)-(1,2,3,4,5,6-hexafluoro-1,3,5-hexenetriyl)bis[triethylsilane], 5, which was prepared via a Pd(PPh₃)₄/CuI-catalyzed cross-coupling reaction of 3 with (E)-1,2-difluoro-1-iodo-2-triethylsilylethene, 6. Pd(PPh₃)₄/CuI cross-coupling of 7 with iodotrifluoroethene gave (3E,5E,7E)-dodecafluoro-1,3,5,7,9-decapentaene, 8.     

Aerobic copper-catalyzed synthesis of (E)-alkenyl sulfones and (E)-β-halo-alkenyl sulfones via addition of sodium sulfinates to alkynes

Copper-catalyzed sulfonylation of alkynes using sodium sulfinates in air produced regio- and stereoselectively (E)-alkenyl sulfones. When a CuCl catalyst was employed, the hydrosulfonylation proceeded syn-selectively, and (E)-alkenyl sulfones were synthesized in excellent yields. In contrast, the reaction using CuI catalyst produced (E)-β-haloalkenyl sulfones anti-selectively in the presence of potassium halides. Furthermore, the (E)-β-bromoalkenyl sulfones are possible to convert into various alkenyl sulfones by Suzuki–Miyaura coupling.     

Synthetic studies on (−)-FR182877: construction of the ABCD ring system via the intramolecular cycloadditions (2)

Construction of the ABCD ring system of (−)-FR182877 via the intramolecular Diels-Alder (IMDA) reaction and the highly diastereoselective intramolecular hetero-Diels-Alder (IMHDA) reaction is described. The IMHDA reactions of the substrates incorporating the oxabutadiene with the E- or Z-alkene were examined, revealing that the sole product was obtained from both substrates and the E-alkene geometry was found to be crucial to obtaining the desired product.     

Synthesis of conjugated (E,E)-1,3-diene-containing troponoid-based compounds

Through exploration of the electrophilic substitution reaction of 3-((2E,4E)-5-phenylpenta-2,4-dienoyl)-2-hydroxy-2,4,6-cycloheptatrien-1-one (3-((2E,4E)-5-phenylpenta-2,4-dienoyl)tropolone) with halogen and diazonium salts as well as the nucleophilic cyclisation reaction with hydroxylamine hydrochloride and substituted phenylhydrazine hydrochlorides by employing our reliable methods, we have synthesised a series of new (E,E)-1,3-diene-bearing troponoid-based compounds. All the newly synthesised molecules represent an issue of great interest, since the presence of conjugated 1,3-diene moiety can be developed further via other reactions.     

Highly efficient synthesis of 4-trifluoromethylfuran derivatives via a sequential deprotection-annulation reaction

(E)-O-protected-2-trifluoromethyl-1-bromo-1-substituted allylic alcohol reacted with terminal alkynes under Sonogashira reaction condition to give the corresponding (E)-2-en-4-ynoic alcohol derivatives, which was further converted to the corresponding 4-trifluoromethylfuran derivatives via a sequential deprotection-annulation reaction in moderate to excellent yields.     

New synthetic methods for 2,3-diarylacridin-9(10H)-one and (E)-2-aryl-4-styrylfuro[3,2-c]quinoline derivatives

Two new synthetic methodologies for 2,3-diarylacridin-9(10H)-ones were developed. The first one involves the Heck reaction of (E)-3-iodo-2-styrylquinolin-4(1H)-ones with styrenes, leading to (E,E)-2,3-distyrylquinolin-4(1H)-ones, which when heated at high temperatures cyclize in two different ways. Electrocyclization and further in situ oxidation leads to 2,3-diarylacridin-9(10H)-ones, while tautomerization, cyclization by nucleophilic addition and further in situ oxidation produces (E)-2-aryl-4-styrylfuro[3,2-c]quinolines as the main compound. The second method gives only 2,3-diaryl-10-methylacridin-9(10H)-ones and involves the Heck reaction of (E)-3-iodo-1-methyl-2-styrylquinolin-4(1H)-ones and styrenes, leading to (E,E)-1-methyl-2,3-distyrylquinolin-4(1H)-ones, which when heated at high temperatures cyclize through electrocyclization and oxidation processes affording the expected compounds. The structures of all new compounds were established by extensive NMR studies.     

Studies on the radical addition reaction of perfluoroalkyl iodides with 2,3-allenols and the Pd-catalyzed kinetic resolution via Sonogashira coupling reaction

A radical addition reaction promoted by Na₂S₂O₄ of perfluoroalkyl iodides with 2,3-allenols affording E/Z mixtures of 3-iodo-4-perfluoroalkyl-substituted allylic alcohols has been studied. Kinetic resolution with Sonogashira coupling reaction was applied to afford the Z isomer of 3-iodo-4-perfluoroalkyl-substituted allylic alcohol (Z-3) and the E isomer of conjugated enynic diols (E-5) in 39-52% and 22-40% yields, respectively.     

(2-Formyl-1-phenylcyclopropyl)phosphonates as building blocks for (2-aminomethyl-cyclopropyl)phosphonates

A diastereomeric mixture of dimethyl (2-formyl-2-methyl-1-phenylcyclopropyl)phosphonate ((Z)-6, (E)-6) was obtained by thermally induced cyclopropanation of α-methylacrolein with α-diazobenzylphosphonate 5. Application of proline or proline-derived organocatalysts accelerated the reaction, but had a minor effect on the Z/E ratio of 6. By reaction with benzylamine or methyl esters of glycine, (S)-alanine, and (S)-phenylalanine, the Z/E-mixture of 6 was converted into cyclopropylaldimines, which after reduction gave the corresponding N-substituted (2-aminomethyl-cyclopropyl)phosphonates.     

Intramolecular allylation of the azo group of 2-(allylsilyl)azobenzenes and its photocontrol

Pentacoordinate allylsilanes bearing an azobenzene moiety were synthesized and their structures were elucidated. The reaction of allyldifluorosilane (E)-7a with BF₃ · OEt₂ did not proceed, but (E)-7a was allowed to react with a fluoride ion to give tetrafluorosilicate 8a via intramolecular allyl-migration from the silicon atom onto the azo group. Activation of both the nucleophilic and electrophilic parts by the Si⋯N interaction was found to be important for promotion of the allyl-migration reaction. The azobenzene moiety of the allylsilane was reversibly isomerized by photoirradiation. The (Z)-7a formed by photoirradiation of (E)-7a is in a tetracoordinate state in contrast to the (E)-7a, and it did not react with a fluoride ion at all under the conditions where (E)-7a reacted quantitatively. The reactivity was successfully controlled without changing any conditions other than the change of the coordination number of the silicon atom induced by photoirradiation.     

Eleuthesides and their analogs: VII. Synthesis of menthane derivatives by the Diels-Alder reaction of levoglucosenone with (2E,4E)-hexa-2,4-dien-1-yl acetate

The Diels-Alder reaction of levoglucosenone with (2E,4E)-hexa-2,4-dien-1-yl acetate was used to synthesize chiral functionalized derivatives of isopropyl(methyl)cyclohexene fused to a carbohydrate fragment.     

Relaxation in torsional motion of triplet oxirane

The rotational barrier height E_rot in the lowest triplet state oxirane molecule was calculated to be 26.3 kcal/mole using a double zeta basis set with partial geometry optimization. This suggest ldrelaxedrd rotation and the computed e(T₁- E(S_o) + E_rot value is commensurate with the enthalpy change for the oxirane-forming O(³P) + C₂H₄ reaction, thus providing a rationale for the stereochemical features of the reaction.