Ruthenium-catalyzed oxidative cyclization of 1,7-dienes. A novel diasteroselective synthesis of 2,7-disubstituted trans-oxepane diols

The ruthenium-catalyzed oxidation of some representative 1,7-dienes has been investigated. Tetrasubstituted 1,7-dienes are transformed into the corresponding trans-2,7-bis-hydroxyalkyl-oxepanes through an oxidative cyclization process. The process proceeds with an excellent stereoselectivity level.     

Synthesis of dihydrofuroflavonoids via palladium-catalyzed annulation of 1,3-dienes

The palladium-catalyzed annulation of 1,3-dienes by o-iodoacetoxyflavonoids provides an efficient approach to biologically interesting dihydrofuroflavonoids. This reaction is very general, regioselective, and a wide variety of terminal, cyclic, and internal 1,3-dienes can be utilized.     

One-pot synthesis of 1-aryl-3-methyl-1,3-dienes using methallyl(trimethyl)silane and aldehydes and their low temperature (Z)→(E) isomerization induced by sulfur dioxide

2-Methylprop-2-ene-1-sulfonyl fluorides can be easily prepared via the ene reaction of methallylsilanes and SO₂. In the presence of a base, aldehydes and 2-methylprop-2-ene-1-sulfonyl fluorides give 1,3-(E) and (Z)-dienes. Their (Z)→(E) isomerization by classical means fails or leads to their polymerization. It is shown that SO₂ can isomerize 1-aryl-3-methyl-1,3-dienes at low temperature, without formation of sulfolenes (cheletropic addition/elimination). Preliminary mechanistic studies suggest that SO₂ adds to 1,3-dienes forming 1,4-diradical intermediates that are responsible for the (Z)→(E) isomerizations.     

[2+4] vs [4+2] Cycloaddition reactions of o-thioquinones with 1,3-dienes

Under kinetic control, the reaction of o-thioquinones with acyclic 1,3-dienes afforded, as main products, the spiro cycloadducts deriving from the participation of the thiones as dienophiles. Under thermodynamic control, or with cyclic dienes, the thioquinones behave as hetero dienes to give the benzoxathiin derivatives with complete regioselectivity.     

Palladium-catalyzed synthesis of 3-trifluoromethylated 1,3-dienes from acrylate derivatives and BTP

Here we reported a Pd-catalyzed coupling reaction between acrylate derivatives and BTP (2-bromo-3,3,3-trifluoropropene) to access 3-trifluoromethylated 1,3-dienes. The reaction allows the formation of the corresponding products in good to excellent yields and moderate Z/E diastereoisomeric ratios. This method broadens the current toolbox to access 3-trifluoromethylated 1,3-dienes.     

Formation of stereodefined multiply substituted all-cis octatetraenes, tricyclo[4.2.0.0]octa-3,7-dienes and pentalenes via CuCl- or FeCl3-mediated dimerization of 1-lithiobutadienes and 1,4-dilithiobutadienes

Dimerization of 1-lithiobutadienes and 1,4-dilithiobutadienes depended remarkably on the substituents and metal halide reagents. Stereodefined multiply-substituted linear all-cis octatetraenes were prepared in moderate yields via FeCl₃-mediated dimerization of 1-lithiobutadienes, while CuCl induced the dimerization of alkyl-substituted 1,4-dilithio-1,3-dienes to form linear all-cis octatetraenes and tricyclo[4.2.0.0^2,5]octa-3,7-dienes. Interestingly, stereodefined pentalene derivatives were also obtained when 1,4-dilithio-1,3-dienes possessed both phenyl and alkyl substituents.     

Nickel-catalyzed acylstannylation and alkynylstannylation of 1,2-dienes

Carbostannylation of 1,2-dienes using acyl- and alkynylstannanes was achieved by means of nickel catalysis. In particular, acylstannylation of 1,2-dienes could be carried out with bis(1,5-cyclooctadiene)nickel [Ni(cod)₂] and acylstannanes to give selectively α-acylmethyl(vinyl)stannanes. The reaction was also applicable to acylstannanes prepared in situ by protonolysis of α-alkoxyalkenylstannanes or by reactions of α-silyloxyvinylstannanes with aldehyde acetals. For alkynylstannylation, a combination of Ni(cod)₂ and 1,3-bis(diphenylphosphino)propane (dppp) was found to be effective to afford α-alkynylmethyl(vinyl)stannanes, whereas the Ni(cod)₂-1,3-bis(dimethylphosphino)propane (dmpp) catalyst switched the regioselectivity to give (Z)-α-alkynylmethyl(alkenyl)stannanes. The acylstannylation products were successfully converted into various conjugated or unconjugated enones by a combination of cross-coupling and NaH-catalyzed isomerization. The alkynylstannylation products were transformed by cross- or homo-coupling reactions to various enynes or 2,3-bis(alkynylmethyl)-1,3-dienes, versatile precursors for variously substituted polycyclic compounds.     

Ti-catalyzed cross-cyclomagnesiation of 1,2-dienes in the stereoselective synthesis of insect pheromones

The Ti-catalyzed intermolecular cross-cyclomagnesiation reaction of aliphatic and oxygenated 1,2-dienes with Grignard reagents was used as the key step to develop facile stereoselective methods for preparation of the major components of citrus leafminer moth (Phyllocnistis citrella) pheromones as well as cotton pink bollworm (Pectinophora gossypiella) and fruit fly (Drosophila melanogaster) attractants.     

Palladium-catalyzed asymmetric hydrosilylation of 1,3-dienes

Advances in the palladium-catalyzed asymmetric hydrosilylation of 1,3-dienes are presented according to substrate types and chiral monophosphine ligands. Chiral monodentate phosphine ligands with a binaphthyl moiety have been proven to be the most efficient ligands for cyclic 1,3-dienes, and planar chiral ferrocenylmonophosphine ligands with two ferrocenyl moieties for linear 1,3-dienes. The ferrocenylmonophosphine ligands have expanded the substrate scope to 1,3-enynes in the asymmetric hydrosilylation. Palladium-catalyzed asymmetric hydrosilylation of 1,3-dienes and 1,3-enynes leads to the stereoselective synthesis of allylsilanes and allenylsilanes, respectively.     

Cycloaddition reactions of 2,4-diphenyl-1,3-diazabuta-1,3-dienes with isocyanates and isothiocyanates

The cycloaddition reactions of 1-p-tolyl and 1-benzyl- 2,4-diphenyl-1,3-diazabuta-1,3-dienes with a variety of aryl and alkyl isocyanate and isothiocyanate are described. The reaction mechanism is also discussed.     

N,N-dihalophosphoramides-XV: The addition of diethyl N,N-dichlorophosphoroamidate (DCPA) to conjugated 1,3-dienes

The addition of DCPA to several conjugated 1,3-dienes has been studied. The reaction was found to proceed in dichloromethane and was spontaneously or photolytically initiated depending on the structure of the dienes. N-chloro adducts, formed upon addition, could be reduced “in situ” with sodium sulphite solution to give the corresponding diethyl N-(chloroalkenyl)posphoroamidates. Addition of DCPA to terminal double bond 1,3-dienes (butadiene, isoprene and 2,3-dimethyl-1,3-butadiene) leads regiospecifically to (E)-1,4-adducts. Similarly, 1,4-addition is also observed for 1,3-cyclohexadiene. Reaction of DCPA with nonterminal double bond 1,3-dienes (trans-piperylene, 4-methyl-1,3-pentadiene, 2,5-dimethyl-2,4-hexadiene and 1,4-diphenyl-1,3-butadiene) usually affords a mixture of adducts. Spectral data and chemical transformations pertinent to the proof of structure of DCPA addition products are presented. A possible mechanism for the addition is discussed.     

Catalytic cycloisomerisation of 1,6-dienes in ionic liquids

The ruthenium and palladium catalysed cycloisomerisation of 1,6-dienes in [bdmim][PF₆], a room temperature ionic liquid (RTIL), is presented. The catalytic system comprising of [RuCl₂(COD)]_n in the presence of ⁱPrOH was found to be particularly efficient and selective for the cycloisomerisation of the N,N-diallyltosylamide. This system can be reused several times without loss of performances and displays catalytic activity after a long storage period in the IL.     

Alcohols controlled selective radical cyclization of 1,6-dienes under mild conditions

An efficient procedure for the selective preparation of hydroxy-, carbonyl- and acetal-containing 2-pyrrolidinones has been developed through radical cyclization of 1,6-dienes initiated by α-C(sp³)–H functionalization of alcohols. This protocol could be conducted at catalyst-free conditions at relatively low temperature (80 °C) by employing commercially available tert-butyl peroxybenzoate (TBPB) as the oxidant.     

Well-defined transition metal complexes with phosphorus and nitrogen ligands for 1,3-dienes polymerization

This article provides an overview on recent progress in the polymerization of 1,3-dienes catalyzed by transition metal complexes with phosphorus and nitrogen ligands. Polymers having different microstructures (cis-1,4; 1,2; mixed cis-1,4/1,2) and tacticity (iso- or syndiotactic) were obtained from various 1,3-dienes (1,3-butadiene, isoprene, 1,3-pentadienes, 1,3-hexadienes) depending on the catalyst used, clearly suggesting that the catalyst structure (i.e. metal nature, type of ligand) strongly affects the polymerization chemo- and stereoselectivity. However, as indicated by the results obtained in the polymerization of substituted butadienes, a fundamental role in determining the selectivity is also played by the type of monomer: polymers with different structure, some of them completely new, were obtained from different monomers with the same catalyst. All these observations permitted to confirm, and in some cases to improve, the knowledge on the diene polymerization mechanism.     

Cross-metathesis of 1,3-dienes with electron-deficient olefins

Cross-metathesis reactions between 1,3-dienes and electron-deficient olefins have been investigated. Terminal monosubstituted 1,3-dienes afforded low yields of the desired CM products due to competing cleavage of the internal double bond. This undesired cleavage is successfully suppressed in the case of 1,3-dienes containing a sterically more congested internal double bond. Methyl vinyl ketone as the coupling partner was shown to provide the best yields.     

Synthesis of 1,1-bisphosphono-2-aza-1,3-dienes, a new class of electron-deficient azadienes

1,1-Bisphosphono-2-aza-1,3-dienes are formed by 1,4-dehydrohalogenation of the corresponding N-(bisphosphonomethyl)-α-haloimines in moderate to good yields. The precursors could be formed by condensation of bisphosphono-amines and the corresponding α-haloaldehydes.     

Perruthenate ion. Another metal oxo species able to promote the oxidative cyclisation of 1,5-dienes to 2,5-disubstituted cis-tetrahydrofurans

Perruthenate ion, from tetrapropylammonium perruthenate (TPAP), in the presence of tetrabutylammonium periodate (TBAPI) as reoxidant catalyses the stereospecific and stereoselective oxidative cyclisation of 1,5-dienes to cis-2,5-disubstituted tetrahydrofurans in good to moderate yields. NMO also works as co-oxidant in the process but is less effective and at least 0.7 equiv TPAP are required. Acidic conditions promote the formation of THF diols. 1,5-Dienes with two terminal double bonds give poor yields of THF’s or cleavage products.     

Nickel-catalyzed amination of 1,3-dienes Evidence for a π-allyl intermediate

syn-π-Crotylbis(triethyl phosphite) nickel hexafluorophosphate reacts with morpholine to give 1-(N-morpholino)-2-butene. This π-crotylnickel complex, without added acid, catalyzes the reaction of butadiene with morpholine. From these observations, π-allyl intermediates are proposed as intermediates in the amination of 1,3-dienes. trans-1,3-Pentadiene reacts with amines more easily than the cis-isomer. The different reactivities are discussed on the basis of the stability of π-allyl complexes which are assumed to be key intermediates.     

Novel synthesis of o-naphthothiophenequinone derivatives via regioselective Diels-Alder reaction

A novel procedure to construct o-naphthothiophenequinones has been achieved from readily available o-benzothiophenquinones and N-dienes via Diels-Alder reaction-aromatization sequence as key steps. The absolute regioselectivity was established via Diels-Alder reaction of o-benzothiophenquinones with rich electron N-dienes.     

Stereoselective synthesis of cis-2,6-bis-hydroxyalkyl-tetrahydropyrans by the permanganate promoted oxidative cyclisation of 1,6-dienes

The first examples of permanganate promoted oxidative cyclisations of 1,6-dienes are described, providing exclusively cis-2,6-bis-hydroxyalkyl-tetrahydropyrans. In addition, good levels of asymmetric induction have been attained using dienoyl sultam substrates.