Stereocontrolled 1,3-phosphatyloxy and 1,3-halogen migration relay toward highly functionalized 1,3-dienes

A double migratory cascade reaction of α-halogen-substituted propargylic phosphates to produce highly functionalized 1,3-dienes has been developed. This transformation features 1,3-phosphatyloxy group migration followed by 1,3-shifts of bromine and chlorine as well as the unprecedented 1,3-migration of iodine. The reaction is stereodivergent: (Z)-1,3-dienes are formed in the presence of a copper catalyst, whereas gold-catalyzed reactions exhibit inverted stereoselectivity, producing the corresponding E products.     

Tetracyanoethylene pi-complex chemistry. Indirect spectrophotometric determination of Diels-Alder-active 1,3-dienes

An indirect spectrophotometric method, based on the rapid Diels-Alder reaction between cisoid 1,3-dienes and tetracyanoethylene (TCNE) and the destruction of an aromatic-TCNE pi-complex, was developed to determine eleven 1,3-dienes in the 0.05-1.00 x 10(-3)M range. These dienes were: cyclopentadiene; 1,3-cyclohexadiene; trans-1,3-pentadiene; 2,4-dimethyl-1,3-pentadiene; trans-2-methyl-1,3-pentadiene; 2-methyl-1,3-butadiene; 9-methylanthracene; 9,10-dimethylanthracene; 1,6-diphenyl-1,3,5-hexatriene; 2,3-dimethyl-1,3-butadiene; and 1,4-diphenyl-1,3-butadiene. Three 1,3-dienes were determined in the 0.05-1 x 10(-4)M range: cyclopentadiene, trans-2-methyl-1,3-pentadiene, and anthracene. The limit of detection for cyclopentadiene in carbon tetrachloride solutions is 0.11 microg/ml. Fourteen 1,3-dienes were found to form stable pi-complexes and could not be determined by the proposed method. For these 1,3-dienes, the spectra of some of the complexes are reported; in addition, relative equilibrium constants for the pi-complexes of 2,5-dimethyl-2,4-hexadiene, cis-1,3-pentadiene, 4-methyl-1,3-pentadiene, and 1,3-cyclo-octadiene were estimated. An explanation of the transient colour in the 1,3-diene-TCNE Diels-Alder reaction is suggested.     

Domino reaction of 1,3-bis(trimethylsilyloxy)-1,3-dienes with oxalyl chloride: general and stereoselective synthesis of gamma-alkylidenebutenolides

The Lewis acid catalyzed cyclization of oxalyl chloride with 1,3-bis(trimethylsilyloxy)-1,3-dienes 3, derived from 1,3-dicarbonyl compounds 1, provides a new and general approach for the synthesis of gamma-alkylidenebutenolides 4, a pharmacologically and synthetically important class of substances. A variety of butenolides were efficiently prepared in good yields and with very good regio- and stereoselectivities. An up-scaling of the reaction was possible. The use of the Lewis acid trimethylsilyl-trifluoromethanesulfonate (TMSOTf) proved to be superior to other activation conditions. Sterically undemanding gamma-alkylidenebutenolides could be prepared alternatively by reaction of the corresponding 1,3-dicarbonyl dianions with N,N'-dimethoxy-N,N'-dimethylethanediamide (2d). In contrast to the dianion method, the Lewis acid catalyzed reaction also facilitated the cyclization of sterically hindered, base-labile, cyclic and functionalized substrates. From a methodology viewpoint, the dianion reaction represents the first cyclization of a bis-Weinreb amide and the first cyclization of an oxalic acid-synthon with an ambident dianion. The TMSOTf-catalyzed reactions are both the first cyclizations of 1,3bis(trimethylsilyloxy)-1,3-dienes with a C2 dielectrophile and the first cyclizations of 1,3-bis(trimethylsilyloxy)-1,3-dienes with a carboxylic acid dichloride or a related dielectrophile.     

Facile route to 1-phosphoryl- and 1-sulfonyl-1,3-dienes via palladium-catalyzed elimination of allylic acetates

The palladium(II)-catalyzed chloroacetoxylation of 1,3-dienes is employed to prepare 1-chloro-4-acetoxy-2-alkenes which are then transformed into 1-phosphoryl- or 1-sulfonyl-4-acetoxy-2-alkenes respectively. Elimination of acetate is promoted by palladium(O)-catalysis or by sodium hydride, producing the useful 1-phosphory]- or 1-sulfonyl-1,3-dienes.     

Synthesis of 2-benzoyl-4-(2-hydroxybenzoyl)phenols by catalytic domino ‘Michael-retro-Michael-Mukaiyama-aldol’ reactions of 1-aryl-1,3-bis(silyloxy)buta-1,3-dienes with 3-formylchromones

The domino reaction of 1-aryl-1,3-bis(silyloxy)buta-1,3-dienes with 3-formylbenzopyrylium triflates, in situ generated from 3-formylchromones, afforded a variety of 2-benzoyl-4-(2-hydroxybenzoyl)phenols.     

Preparation of partially substituted 1-halo- and 1,4-dihalo-1,3-dienes via reagent-controlled desilylation of halogenated 1,3-dienes

Depending on the desilylation reagents used, 1-halo-1,4-bis(trimethylsilyl)-1,3-butadienes afforded either 1-halo-1-trimethylsilyl-1,3-butadienes or 1-halo-4-trimethylsilyl-1,3-butadienes in excellent yields with excellent selectivity, respectively, when treated with CF3COOH or with NaOMe. These monosilylated 1,3-butadiene products could be further desilylated to generate their corresponding halobutadienes via the above reagent-controlled desilylation reaction. When 1,4-dihalo-1,4-bis(trimethylsilyl)-1,3-dienes were treated with MeONa/MeOH at room temperature, desilylation of both of the two trimethylsilyl groups took place to afford their corresponding 1,4-dihalo-1,3-dienes in excellent yields. The commonly used desilylation reagent CF3COOH did not work for these dihalobutadienes.     

Heterocyclen-synthesen mit 4,4-bis(trifluormethyl)-1,3-diazabuta-1,3-dienen, II [1] spektroskopische untersuchung der isonitril- und dimethoxy-carben-addukte

[4+1] Cycloaddition reactions of 4,4-bis(trifluoromethyl)-1,3-diazabuta-1,3-dienes 3, accessible by reaction of amidines with hexafluoroacetone in the presence of dehydrating reagents, with isonitriles and dimethoxycarbene are described. Configuration of the isonitrile adducts 5 – 9 can be determined on basis of the ¹⁹F NMR data.     

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.     

Cycloaddition reactions of 1-lithio-1,3-dienes with aromatic nitriles affording multiply substituted pyridines, pyrroles, and linear butadienylimines

Fully or partially substituted 1-iodo- or 1-bromo-1,3-dienes could be readily lithiated using t-BuLi or n-BuLi to afford their corresponding 1-lithio-1,3-diene derivatives in quantitative yields. When these in situ generated lithium reagents were treated with organonitriles, depending on the substitution patterns of the butadienyl skeletons, substituted pyridines, pyrroles, and/or linear butadienyl imines were formed in good to excellent yields via N-lithioketimine intermediates. In the cases of 1,2,3,4-tetrasubstituted and 2,3-disubstituted 1-lithio-1,3-dienes, pyridine derivatives or linear butadienyl imines were generally formed depending on the reaction temperatures. When 1,2,3,4-tetrasubstituted 4-halo-1-lithio-1,3-dienes and 1,2-disubstituted 1-lithio-1,3-dienes were treated with organonitriles, pyrrole derivatives or linear butadienyl imines were obtained. Competition between 5-exo and 6-endo cyclization was found to be responsible for the formation of either pyrroles or pyridines. Selective elimination of RLi from the lithiated cyclic N-containing intermediates was observed. The order of elimination was found to be LiCl > Me3SiLi > LiH.     

Efficient one-to-one coupling of easily available 1,3-dienes with carbon dioxide

An efficient one-to-one coupling reaction of atmospheric pressure carbon dioxide with 1,3-dienes is realized for the first time through PSiP-pincer type palladium-catalyzed hydrocarboxylation. The reaction is applicable to various 1,3-dienes including easily available chemical feedstock such as 1,3-butadiene and isoprene. This protocol affords a highly useful method for the synthesis of β,γ-unsaturated carboxylic acid derivatives from CO(2).     

A highly stereoselective synthesis of (E)-1-substituted-1,3-dienes

(E)-1-substituted-1,3-dienes are obtained with high stereoselectivity by the thermal extrusion of SO₂ from 2-substituted-2,5-dihydrothiophene-1,1-dioxides generated by a retro Diels-Alder reaction. An application to the synthesis of (E)-9,11-dodecadien- 1-yl acetate, a sex pheromone of the red-bollworm moth is described.     

Mechanistic and synthetic aspects of 2-aza-1,3-diene preparation through N-(1-triethylsilylallyl)imine protodesilylation

Features of a novel method for preparation of 2-aza-1,3-dienes involving CsF induced protodesilylation of N-(1-triethylsilylallyl)imines is described.Substances containing the 2-aza-1,3-diene grouping represent a unique class of compounds as a result of their potentially interesting excited- and ground- state chemistry. Particularly significant is the Diels-Alder reactivity of these substances.¹ Several procedures with varying and often limited generality have been developed to prepare 2-aza-1,3-dienes.² In recent efforts designed to explore the chemistry of 2-aza-1,3-dienes,^1c we have explored a potentially versatile method to prepare these substances (Scheme 1) involving N-(1-trialkylsilylallyl)-imine protodesilylation reactions.     

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.     

3,3,3-trichloropropyl-1-triphenylphosphorane: a reagent for the synthesis of (Z)-1,3-enynes, (Z,Z)-1-chloro-1,3-dienes, and 1,3-diynes

3,3,3-Trichloropropyl-1-triphenylphosphonium chloride is conveniently prepared from 2-chloroethanol, triphenylphosphine, and trichloroacetic acid. Deprotonation of this reagent generates 3,3,3-trichloropropyl-1-triphenylphosphorane, which reacts with aldehydes to give trichloromethylated (Z)-olefins, which are useful for the synthesis of (Z)-1,3-enynes, (Z,Z)-1-chloro-1,3-dienes, and 1,3-diynes in high yields and stereospecificities.     

Palladium-catalyzed Heck reaction on 1-alkoxy-1,3-dienes: a regioselective gamma-arylation of alpha,beta-unsaturated carbonyl compounds

[reaction: see text] alpha,beta-Unsaturated acetals afford, in the presence of the LIC-KOR superbase, 1-alkoxybuta-1,3-dienes. These substrates cross couple with aryl derivatives in the presence of Pd catalyst (Heck conditions) in a regio- and stereoselective mode. With dialkyl acetals, the reaction affords arylated dienes; on the other hand, in the case of 1,3-dioxane derivatives, the final outcome of the process formally corresponds to the direct gamma-arylation reaction of the starting alpha,beta-unsaturated material.     

Synthesis of dihydrofurocoumarins via palladium-catalyzed annulation of 1,3-dienes by o-iodoacetoxycoumarins

[reaction: see text] A variety of biologically interesting dihydrofurocoumarins have been synthesized in high yields by the palladium-catalyzed annulation of 1,3-dienes by o-iodoacetoxycoumarins. This reaction is very general and regioselective, and a wide variety of terminal, cyclic, and internal 1,3-dienes can be utilized.     

A facile synthesis of 1-fluoro-1-halogenoalka-1,3-dienes

1-Fluoro-1-halogenoalka-1,3-dienes are synthesized in good yields by treatment of 2,2-dihalogenocyclopropyl carbinols with (HF)_n.Py in the presence of diisopropylamine and NaF followed by dehydrohalogenation with potassium t-butoxide.     

Stereoconvergent Synthesis of Z-1,3-Disubstituted-1,3-Dienes by Uphill Photocatalysis

A variety of 1-aryl-1,3-dienes were isomerized from E to Z isomers by photocatalysis using Ru(bpy)₃[PF₆]₂ and blue LED light. Enrichment of the Z-isomer is thought to occur by selective triplet energy transfer from the photocatalyst to the stereoisomeric mixture. The 1,3-diene starting materials are easily made by catalytic ene-yne metathesis (EYM). To access 1,3-diene Z-stereoisomers directly, a one pot procedure was developed. Additional 1,3-dienes were investigated for both isomerization and Z-enrichment. The combination of cross EYM with photocatalysis allows for the stereoconvergent synthesis of Z-1,3-dienes.     

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.     

Nickel-catalyzed enantioselective three-component coupling of bis-1,3-dienes, aldehydes, and dimethylzinc

Nickel-catalyzed three-component coupling of bis-1,3-dienes, aldehyde, and dimethylzinc was investigated. In the presence of catalytic amounts of Ni(acac)2 and PPh3, bis-1,3-dienes smoothly react with an aldehyde and dimethylzinc via intramolecular cyclodimerization of bis-1,3-diene moiety. The reaction proceeds through formation of a cyclic bis-allylnickel complex, insertion of an aldehyde, and addition of dimethylzinc to the resulting oxanickellacycle intermediate. An enantioselective coupling was also achieved by the use of a chiral monodentate phosphine ligand, H-MOP.