Cu(I)-catalyzed cycloguanidination of olefins

This paper describes a novel cycloguanidination process using CuCl as catalyst and diaziridinimines as the nitrogen source. A variety of conjugated dienes, trienes, and terminal olefins can be effectively diaminated under mild reaction conditions. For dienes and trienes, the reaction occurs at the terminal double bond with high regioselectivity.     

Some new dienophiles in the diels-alder reaction with active cyclic dienes

A comparative study of the Diels-Alder reaction have been carried out for three types of cyclic dienes: cyclopentadiene (CPD), hexachlorocyclopentadiene (HCP), and tetrachloro-1,2-benzoquinone (TCBQ) with dienophiles of five types: monosubstituted acetylenes (propargyl alcohol and its esters), conjugated amines (allyl acetylene, allyl ethynyldimethylcarbonol and its esters), conjugated dienes (2-methylhexadiene-3,5-ol-2 and its esters, 1-ethoxy- and 1-ethoxycarbonylbutadiene-1,3), and conjugated trienes (hexatriene-1,3,5 and 5-methylhexatriene-1,3,5).It was found that conjugated trienes react with dienes of all types under mild conditions and give only the monoadducts through the terminal vinyl or ethynyl group.     

Gold(I)-catalysed synthesis of conjugated trienes

Gold(I)-catalysed reaction between cyclopropenes and furans produces functionalised conjugated trienes. The reaction is mild, facile and proceeds with very low catalyst loadings.     

Efficient method to locate double bond positions in conjugated trienes

The double bond positions of 11 conjugated trienes were unambiguously located through a simple derivatization method amenable to nanogram-scale analyses. The trienes were reacted with the powerful dienophile 4-methyl-1,2,4-triazoline-3,5-dione (MTAD), and the mass spectra of the resulting cycloadducts exhibited large diagnostic fragments which allowed the unequivocal location of the double bonds in the parent triene in most cases. Catalytic hydrogenation of the cycloadducts produced saturated compounds with characteristic mass spectral fragments from which the positions of the trienes in the parent compounds could be readily confirmed. Application of the method was demonstrated by the microscale identification of two conjugated triene and one conjugated diene components from extracts of the sex pheromone gland of the saturniid moth Automeris cecrops pamina.     

Consecutive Rh(I)-catalyzed Alder-ene/Diels-Alder/Diels-Alder reaction sequence affording rapid entry to polycyclic compounds

Conversion of acyclic allenynes to polycyclic compounds using consecutive transition metal catalyzed carbon-carbon bond forming reactions in a single chemical operation is described. Reaction of an allenyne with a Rh(I) catalyst affords a cross-conjugated triene via a formal Alder-ene reaction. The triene then participates in a Rh(I)-catalyzed intramolecular [4+2] cycloaddition reaction to generate a new conjugated diene. An external dienophile is added to this diene which then undergoes a second [4+2] cycloaddition reaction to afford a complex polycyclic ring system. This reaction sequence demonstrates the synthetic potential of allenynes and cross conjugated trienes and highlights the rapid increases in molecular complexity that are possible by one-pot sequential transition metal catalyzed carbon-carbon bond forming reactions.     

Synthesis of highly substituted 1,3-dienes and 1,3,5-trienes by the palladium-catalyzed coupling of vinylic halides,internal alkynes,and organoboranes

[reaction: see text] Highly substituted 1,3-dienes and trienes have been prepared in good to excellent yields by the palladium-catalyzed coupling of vinylic halides, internal alkynes, and organoboranes.     

Studies on thermal reactivity of beta-(1,2-allenyl)butenolides and 2-allyl-3-allenylcyclohex-2-enones

A series of thermal pericyclic reactions of beta-allenylfuranones have been studied. It was observed that beta-allenylfuranones would undergo 1,5-hydrogen shift to afford a new type of trienes upon heating. Due to their high reactivity, these trienes would undergo subsequent pericyclic reactions based on the nature of the substituent group R: When R is an alkyl group, the intermediate 4a or 4b would undergo a further 1,7-hydrogen shift to afford a more stable conjugated triene 3; with R being phenyl or cyclopropyl group, the 1,7-hydrogen shift was inhibited and the 4-type conjugated triene would form a six-membered ring 5 via 6 pi-electrocyclization. Interestingly, introducing another C=C double bond into the triene intermediate (R = CH=CH2, the 18-type intermediate would undergo 8 pi-electrocyclization reaction to form an eight-membered ring. Such a transformation was also observed with 2-allyl-3-allenylcyclohex-2-enones. The deuterium-labeling mechanistic studies show that the alkyl groups at the allenyl moiety of 1 participated in the isomerization process via 1,7-hydrogen shifts between 18 A, 20 A, and 29 A.     

Diastereoselective ring-closing metathesis: synthesis of P-stereogenic phosphinates from prochiral phosphinic acid derivatives

[reaction: see text] The preparation of phosphorus-containing trienes featuring two diastereotopic vinyl moieties followed by a diastereoselective ring-closing metathesis is described. This methodology allowed for the synthesis of novel highly functionalized P-stereogenic heterocycles featuring both an exo- and an endocyclic double bond. An investigation into the factors influencing the diastereochemical outcome of the ring-closing metathesis is also presented, revealing that the geometry of the double bonds conjugated to phosphorus is important and that 1,3-stereoinduction is superior to 1,4-stereoinduction for these reactions.     

Biomimetic cationic polyannulation reaction catalyzed by Bi(OTf)3: cyclization of 1,6-dienes, 1,6,10-trienes, and aryl polyenes

Nonactivated trienes and aryltrienes were cyclized into polycyclic compounds in good to excellent yields under bismuth triflate catalysis in a biomimetic fashion. The reaction showed broad applicability and allowed for the formation of functionalized bicyclic to tetracyclic structures from simple precursors in one pot. For some specific substrates, the cyclization was followed by a methyl shift as encountered in terpenoid biosynthesis.     

INDO calculations on the sigmatropic [1, 5] H-Shift in 1,3-cyclohexadiene and 1,3,5-cycloheptatriene A homo-cyclopentadienyl transition state model

INDO calculations have been performed for the activated complex of the [1, 5] H.-shift in 1,3-cyclohexadiene and 1,3,5-cycloheptatriene. During the migration in the cyclohexadiene system a homoconjugation was calculated between the carbon atoms C₁ and C₅. For cycloheptatriene it could be demonstrated that one double bond does not participate in the reaction. Activation enthalpies are related to (homo)conjugation in the transition state of the reaction for cyclic conjugated dienes and trienes. The electron density on the migrating hydrogen can be related to the electron affinity of the ring system in the transition state.[/p]     

Effects of wavelength and conformation on the photochemistry of vitamin D and related conjugated trienes

Irradiation experiments under various conditions establish that the photoreactions of conjugated trienes are governed by the ground state conformational equilibrium and the NEER principle, as well as by the wavelength dependent relaxation behaviour of the excited species.     

Diamination of conjugated dienes and trienes catalyzed by N-heterocyclic carbene-pd(0) complexes

This paper describes a diamination process using di-t-butyldiaziridinone as nitrogen source and N-heterocyclic carbene-Pd(0) complex as catalyst. A wide variety of conjugated dienes and trienes can be effectively diaminated in good yields with high regio- and stereoselectivities.     

Stereoselective Synthesis of Substituted 1,3,5,7,9-Decapentaenes

Conjugated 1,3,5,7,9-decapentaene is an important structural unit in various of natural products such as phytoene, aurenin, vitamin At and A2[1]. It has been shown that conjugated polyenes are potentially useful compounds for non-linear optical materials. In the meantime the study of well-defined molecules has advanced into a strong field on its own right, because of the promising electronic and optical properties of these compounds[2]. It also attracts the interests of physical chemists as a calculation model[3] during the past decades. In the literature, there are only a few general strategies for the stereocontrolled construction of the decapentaene unit. This is mainly due to the instability and the facile (E)-(Z) isomerization of pentaene system. Synthetic methods for the construction of conjugated decapentaenes relied on the Wittig olefination[4], the Heck coupling reaction[5], the mixed crossed aldol condensation between conjugated esters and aldehydes[6], opening reaction of fulvalene complexes[7]. In our previous studies[8] on stereoseletive synthesis of polyene, we reported that conjugated trienes and enediynes could be prepared by our modified Ramberg-Backlund reaction from corresponding diallylic sulfones and dipropagylic sulfones. This synthetic method was applied to the synthesis of natural products containing a conjugated triene unit such as Galbanolenes. Reported here are our finding that bis-dienylic sulfones when submitted our Ramberg-Backlund conditions, provide decapentaenes in good yield. We use this synthetic method to synthesize 1,3,5,7,9-dec apentaene.     

On the Effect of Diene Geometry in Intramolecular Allyl Cation Cycloadditions

Attempted intramolecular allyl cation cycloaddition of trienol 2a, which contains a conjugated diene of Z-configuration, affords monocyclic trienes 3a,b, in contrast to related trienols known to produce [5,5]-bicyclic and/or [5,7]-bicyclic products. Cyclopentyl trienes 3a,b are isomeric with multifidene, an algal pheromone. Dimethyl trienol 6 fails to cyclize (under identical conditions), but eliminates to yield tetraene 7.     

Intramolecular Diels-Alder reactions using chiral ruthenium Lewis acids and application in the total synthesis of ent-ledol

One-point binding chiral ruthenium Lewis acids incorporating the C(2)-symmetric electron-poor bidentate phosphinite ligand BIPHOP-F and a Cp or an indenyl 'roof' can efficiently catalyze asymmetric intramolecular Diels-Alder reactions of trienes to form bicyclic adducts with good to excellent asymmetric induction. This reaction forms the key step in a total synthesis of ent-ledol in 96% ee. The synthesis also helps to clarify the stereochemical assignment of ledol and inconsistencies in the measured optical rotation.     

Stereospecific 1,4-cis-hydrogenation of conjugated dienes,dienynes, and dienediynes catalyzed by chromium carbonyl complexes in stereocontrolled syntheses of physiologically active olefins

Synthesis of insect pheromones provides a good illustration of versatility, flexiblility, and practical convenience of the chromium carbonyl complexes-mediated 1,4-cis-hydrogenation of conjugated dienes as the tool for for stereocontrolled construction of di-, tri-, and tetrasubstituted olefins and nonconjugated dienes. A new strategy for synthesizing homoconjugated all-Z-dienes and trienes by hydrogenation of diene-alkyne conjugated systems using the same catalysts is proposed.     

An atom-economical approach to conformationally constrained tricyclic nitrogen heterocycles via sequential and tandem Ugi/intramolecular Diels-Alder reaction of pyrrole

An efficient approach to rigid tricyclic nitrogen heterocycles via sequential and tandem Ugi/intramolecular Diels-Alder (IMDA) cycloaddition of pyrrole is described. The one-pot Ugi four-component condensation (4CC) reaction was used as the key transformation to prepare trienes with a carboxamide substituent on the tether. The use of acrylic acid (21) and N-propyl- and N-benzylmaleamic acids (24b and 24C) as the acid components provided trienes 22, 25b, and 25c, respectively, which upon heating at 120 degrees C for 12 h yielded the corresponding [4 + 2] cycloaddition products. In the case of maleic acid derivative 24a, heating the reaction mixture at 60 degrees C for 6 h promoted the cycloaddition reaction and provided the desired product 26a in 78% yield. In contrast, fumaric acid monoethyl ester (27a) and 3-acetyl- and 3-(4-methylbenzoyl) acrylic acids (27b-c) directly yielded the corresponding Ugi/IMDA cycloaddition products 29a-c in high yields at room temperature without any trace of initially formed trienes 28a-c. The IMDA cycloaddition reactions proceed with excellent stereoselectivity with the formation of five stereogenic centers and three rings.     

Synthesis of dispirocyclohexadiene bisoxindole from Morita-Baylis-Hillman carbonate of isatin

6π-Electrocyclization of conjugated trienes derived in-situ from the Morita-Baylis-Hillman carbonates of N-methylisatins afforded dispirocyclohexadiene bisoxindoles in good yields. Two stereoisomers (cis and trans) were formed in almost equal amounts.     

Transition-Metal Catalysis of Triene 6π Electrocyclization: The π-Complexation Strategy Realized

Triene 6π electrocyclization, wherein a conjugated triene undergoes a concerted stereospecific cycloisomerization to a cyclohexadiene, is a reaction of great historical and practical significance. In order to circumvent limitations imposed by the normally harsh reaction conditions, chemists have long sought to develop catalytic variants based upon the activating power of metal–alkene coordination. Herein, we demonstrate the first successful implementation of such a strategy by utilizing [(C₅H₅)Ru(NCMe)₃]PF₆ as a precatalyst for the disrotatory 6π electrocyclization of highly substituted trienes that are resistant to thermal cyclization. Mechanistic and computational studies implicate hexahapto transition-metal coordination as responsible for lowering the energetic barrier to ring closure. This work establishes a foundation for the development of new catalysts for stereoselective electrocyclizations.     

Transition‐Metal Catalysis of Triene 6π Electrocyclization: The π‐Complexation Strategy Realized

Triene 6π electrocyclization, wherein a conjugated triene undergoes a concerted stereospecific cycloisomerization to a cyclohexadiene, is a reaction of great historical and practical significance. In order to circumvent limitations imposed by the normally harsh reaction conditions, chemists have long sought to develop catalytic variants based upon the activating power of metal–alkene coordination. Herein, we demonstrate the first successful implementation of such a strategy by utilizing [(C₅H₅)Ru(NCMe)₃]PF₆ as a precatalyst for the disrotatory 6π electrocyclization of highly substituted trienes that are resistant to thermal cyclization. Mechanistic and computational studies implicate hexahapto transition‐metal coordination as responsible for lowering the energetic barrier to ring closure. This work establishes a foundation for the development of new catalysts for stereoselective electrocyclizations.