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Although the reaction of heterosubstituted allylic carbanions (2) with aldehydes generally produces a mixture of the γ- and α-adducts (4 and 3), syn-3 and anti-3 can be prepared either exclusively or predominantly by the proper choice of the organometallic compound added.

We report the first stereoconvergent Markovnikov 1,2-hydrosilylation of conjugated dienes using catalysts generated from bench-stable Co(acac)2 and phosphine ligands. A wide range of E/Z-dienes underwent this Markovnikov 1,2-hydrosilylation in a stereoconvergent manner, affording (E)-allylsilanes in high isolated yields with high stereoselectivities (E/Z = >99;:;1) and high regioselectivities (b/l up to > 99;:;1). Mechanistic studies revealed that this stereoconvergence stems from a σ-π-σ isomerization of an allylcobalt species generated by the 1,4-hydrometalation of Z-dienes. In addition, a cobalt catalyst that can only catalyze the hydrosilylation of the E-isomer of an (E/Z)-diene was identified, which allows the separation of the (Z)-isomer from an isomeric mixture of (E/Z)-dienes. Furthermore, asymmetric hydrosilylation of (E)-1-aryl-1,3-dienes was studied with Co(acac)2/(R)-difluorphos and good enantioselectivities (er up to 90;:;10) were obtained.

The asymmetric denitrogenative cycloaddition has emerged as a powerful tool to build chiral aza-heterocyles. However, only one example of asymmetric denitrogenative cycloaddition of benzotriazole with unsaturated hydrocarbons has been explored so far, bec

The value of catalytic dehydrogenation of aliphatics (CDA) in organic synthesis has remained largely underexplored. Known homogeneous CDA systems often require the use of sacrificial hydrogen acceptors (or oxidants), precious metal catalysts, and harsh reaction conditions, thus limiting most existing methods to dehydrogenation of non- or low-functionalized alkanes. Here we describe a visible-light-driven, dual-catalyst system consisting of inexpensive organophotoredox and base-metal catalysts for room-temperature, acceptorless-CDA (Al-CDA). Initiated by photoexited 2-chloroanthraquinone, the process involves H atom transfer (HAT) of aliphatics to form alkyl radicals, which then react with cobaloxime to produce olefins and H2. This operationally simple method enables direct dehydrogenation of readily available chemical feedstocks to diversely functionalized olefins. For example, we demonstrate, for the first time, the oxidant-free desaturation of thioethers and amides to alkenyl sulfides and enamides, respectively. Moreover, the system's exceptional site selectivity and functional group tolerance are illustrated by late-stage dehydrogenation and synthesis of 14 biologically relevant molecules and pharmaceutical ingredients. Mechanistic studies have revealed a dual HAT process and provided insights into the origin of reactivity and site selectivity.

We report the first enantioselective addition of pyrazoles to 1,3-dienes. Secondary and tertiary allylic pyrazoles can be generated with excellent regioselectivity. Mechanistic studies support a pathway distinct from previous hydroaminations: a Pd0-catalyzed ligand-to-ligand hydrogen transfer (LLHT). This hydroamination tolerates a range of functional groups and advances the field of diene hydrofunctionalization.

A photoinduced palladium-catalyzed 1,2-carbofunctionalization of conjugated dienes has been developed. This mild modular approach, which does not require employment of exogeneous photosensitizers and external oxidants, allows for efficient and highly regio- and stereoselective synthesis of a broad range of allylic amines from readily available 1,3-dienes, alkyl iodides, and amines. Employment of O- and C-nucleophiles toward oxyalkylation and dialkylation products was also demonstrated. A putative π-allyl palladium radical-polar crossover path is proposed as a key event in this three-component coupling process. The utility of this protocol is highlighted by its application for derivatization of several amine-containing drugs.

A practical copper-catalyzed highly regioselective 1,2-hydrocarboxylation of terminal 1,3-diene with carbon dioxide has been developed. Under mild reaction conditions, this chemistry afforded 2-benzyl-β,γ-unsaturated acid derivatives as products, which are a kind of important unit for bio-active molecules and versatile precursors for organic synthesis, with good functional group tolerance. The key intermediate in this transformation is illustrated by control experiments.

We report a Pd-catalyzed intermolecular hydrophosphinylation of 1,3-dienes to afford chiral allylic phosphine oxides. Commodity dienes and air stable phosphine oxides couple to generate organophosphorus building blocks with high enantio- and regiocontrol. This method constitutes the first asymmetric hydrophosphinylation of dienes.

A site-selective catalytic incorporation of multiple CO2 molecules into 1,3-dienes en route to adipic acids is described. This protocol is characterized by its mild conditions, excellent chemo- and regioselectivity and ease of execution under CO2 (1 atm), including the use of bulk butadiene and/or isoprene feedstocks.

1,2-Disubstituted alkenes such as vinyl arenes, vinyl silanes, and vinyl boronates are among the most versatile building blocks that can be found in every sector of chemical science. We herein report a noble-metal-free method of accessing such olefins through a photo-induced decarboxylative Heck-type coupling using alkyl carboxylic acids, one of the most ubiquitous building blocks, as the feedstocks. This transformation was achieved in the absence of external oxidants through the synergistic combination of an organo photo-redox catalyst and a cobaloxime catalyst, with H2 and CO2 as the only byproducts. Both control experiments and DFT calculations supported a radical-based mechanism, which eventually led to the development of a selective three-component coupling of aliphatic carboxylic acids, acrylates, and vinyl arenes. More than 90 olefins across a wide range of functionalities were effectively synthesized with this simple protocol.

We report a method for the catalytic, enantioselective intermolecular addition of aliphatic amines to acyclic 1,3-dienes. In most cases, reactions proceed efficiently at or below room temperature in the presence of 5 mol % of a Pd catalyst bearing a PHOX ligand, generating allylic amines in up to 97:3 er. The presence of an electron-deficient phosphine within the ligand not only leads to a more active catalyst but also is critical for achieving high site selectivity in the transformation.

Carbon-supported Pt nanoparticles (Pt/C) were found to be effective heterogeneous catalysts for the direct Julia olefination of alcohols in the presence of sulfones and KOtBu under oxidant-free conditions. Primary alcohols, including aryl, aliphatic, allyl, and heterocyclic alcohols, underwent olefination with dimethyl sulfone and aryl alkyl sulfones to give terminal and internal olefins, respectively. Secondary alcohols underwent methylenation with dimethyl sulfone. Under 2.5 bar H2, the same reaction system was effective for the transformation of alcohol OH groups to alkyl groups. Structural and mechanistic studies of the terminal olefination system suggested that Pt0 sites on the Pt metal particles are responsible for the rate-limiting dehydrogenation of alcohols and that KOtBu may deprotonate the sulfone reagent. The Pt/C catalyst was reusable after the olefination, and this method showed a higher turnover number (TON) and a wider substrate scope than previously reported methods, which demonstrates the high catalytic efficiency of the present method. Olefination of alcohols: The first heterogeneous catalytic terminal and internal olefination of primary alcohols and methylenation of secondary alcohols with sulfones, a reusable carbon-supported Pt catalyst, and KOtBu is reported (see scheme).

The development of semi-stabilized, stabilized, and functionalized ylides derived from short-chain trialkylphosphines in the Wittig-type olefination reactions toward the synthesis of alkenes, including stilbenes, styrenes, and 1,3-dienes, as well as reagents for homologation reactions, are described. The methods allow easy access to alkenes with high (E)-stereoselectivity in good yield. These reactions are conducted with weak bases in aqueous media, which allows easy separation of water-soluble phosphine oxides. The development of a mild organocatalytic process for the Wittig reaction and extension toward the preparation of reporter stilbenes under biological conditions are also described. Applications toward the preparation of biologically active natural products and derivatives are discussed.

A new role of superoxide ion in the isomerization of homobenzylic acetylenes leading to 1-aryl-1,3-butadienes is reported. The unconventional reagent KO2 is found to be superior in performing this kind of isomerization over other the commonly u

The cobalt(I)-catalysed 1,4-hydrovinylation reaction of allyloxytrimethylsilane and allyl alcohol with substituted 1,3-dienes leads to hydroxy-functionalised 1,4-dienes in excellent regio- and diastereoselective fashion. Those 1,4-dienols can be converted

In the asymmetric hydrovinylation (HV) of an E/Z-mixture of a prototypical 1,3-diene with (S,S)-(DIOP)CoCl2 or (S,S)-(BDPP)CoCl2 catalyst in the presence of Me3Al, the (E)-isomer reacts significantly faster, leaving behind the Z-isomer intact at the end of the reaction. The presumed [LCo-H]+-intermediate, especially when L is a large-bite angle ligand, similar to DIOP and BDPP, promote an unusual isomerization of (E/Z)-mixtures of 1,3-dienes to isomerically pure Z-isomers. A mechanism that involves an intramolecular hydride addition via an [η4-(diene)(LCo-H)]+ complex, followed by p-s-p isomerization of the intermediate Co(allyl) species, is proposed for this reaction.

A bioinsipred gold-catalyzed tandem Diels-Alder/Diels-Alder reaction of an enynal and a 1,3-diene, forming the highly-strained benzotricyclo[3.2.1.0 2,7]octane skeleton, was reported. In contrast, a Diels-Alder/Friedel-Crafts tandem reaction occurred instead when silver salts were used as the catalyst. Although both reactions experienced the similar Diels-Alder reaction of a pyrylium intermediate with a 1,3-diene, they have different reaction mechanisms. The former proceeded with a stepwise Diels-Alder reaction, while the latter one with a concerted one. Mother nature knows best! A gold-catalyzed reaction of enynals and 1,3-dienes, giving rapid access to the highly strained benzotricyclo[3.2.1.02,7]octane skeleton, is reported (see scheme; QMD=quinodimethane). Owing to the mild reaction conditions, excellent substrate scope, and high functional-group tolerance, this system holds potential for the construction of complex molecules with the tricyclo[3.2.1.02,7]octane skeleton. Copyright

Unexpected losses in stereochemistry from Stille reactions involving Z-alkenyl halides have been shown to be ligand dependent. A new set of reaction conditions has been developed that, in most cases, leads to highly stereoselective cross-couplings under mild conditions, along with improved yields.

It's do or diaminate: The selective diamination of 1,3-butadienes in the presence of hypervalent iodine reagents has been developed. This oxidation process proceeds with complete selectivity in favor of diamination. Depending on the substrate, it proceeds either with 1,2- or 1,4-regioselectivity (see scheme). Copyright

More with boron: The development of catalytic enantioselective 1,2-diboration of 1,3-dienes enables a new strategy for enantioselective carbonyl allylation reactions (see scheme). These reactions occur with outstanding levels of stereoselection and can be applied to both monosubstituted and 1,1-disubstituted dienes. The carbonyl allylation reactions provide enantiomerically enriched functionalized homoallylic alcohol products. Copyright

A direct synthesis of 1,3-dienes and 1,3,5-trienes from the reaction of semi-stabilized ylides and a range of saturated and unsaturated aldehydes is reported in water as solvent, employing sodium hydroxide as base. The water-soluble phosphine oxide side p

Functionalized arylcopper reagents react readily with alkenyl sulfonates in the presence of catalytic amounts of Fe(acac)3, (10 mol%) providing the expected cross-coupling products in good yields. Ester or cyano group are tolerated. This cross-coupling can be performed with dienyl sulfonates leading to the corresponding substituted dienes. Georg Thieme Verlag Stuttgart.

Products from solvolytic reactions that form the (2-phenylcyclopropyl) carbinyl cation were determined. The majority of products (> 98%) derived from the 1-phenyl-3-butenyl cation, consistent with reports by Wiberg and co-workers. Small amounts of products derived from the 1-phenyl-1- cyclopropylmethyl cation also were found; these products were previously predicted to be formed from reactions of the title cation. Although the 1-phenyl-1-cyclopropylmethyl cation is considerably more stable than the 1-phenyl-3-butenyl cation, it is not kinetically accessible under a variety of solvolytic conditions. Copyright

An extremely simple and efficient palladium-catalyzed coupling procedure for the synthesis of functionalized styrenes and dienes is utilized to demonstrate how 4,4,6-trimethyl-2-vinyl-1,3,2-dioxaborinane can be employed to selectively undergo Suzuki-Miyaura coupling with a range of halide substrates. Georg Thieme Verlag Stuttgart.

Stereoselective dienyl zirconocene derivatives have been prepared via a tandem allylic C-H bond activation isomerization-elimination reaction. These reagents can be either trapped directly with electrophiles or transmetalated to copper to participate in s

Several dienyl zirconocene derivatives were easily prepared, as unique geometrical isomers, from simple non-conjugated unsaturated enol ethers with (1-butene)ZrCp2 complexes. This new methodology is based on a tandem allylic C-H bond activation-elimination sequence and the mechanism has been mapped out by deuterium labeling experiments. The stereochemical outcome of this process was determined by addition of several electrophiles. Moreover, when the organometallic derivative is vinylic as well as allylic such as in 44-47Zr, an unexpected reversal of the stereochemistry has been found during the zirconium to copper transmetalation step.

Treatment of Cp2ZrBu2 with enol ether containing a remote double bond lead to conjugated metalated diene as single isomer via a tandem isomerization-elimination sequence. 2-Arylsulfonyl 1,3-dienes can also be used as a source of dienyl zirconocene derivatives, and the stereochemistry of the diene is dependent on the transmetalation reaction. Copyright

Lithiated allylic phosphonates undergo efficient olefination reactions with a variety of aldehydes in the presence of HMPA to give terminal 1,3-dienes with high selectivity for the E-isomer. This method is general and procedurally simple.

After treatment with an appropriate base (butyllithium or sodium amide), 2-alkenyltris(2-methoxymethoxyphenyl)phosphonium salts carrying an allyl, crotyl, or prenyl (3-methyl-2-butenyl) side chain condense with saturated or unsaturated aldehydes to give conjugated dienes with Z/E ratios ranging from 90:10 to >99:1 and averaging 96:4. Owing to steric congestion, yields are only moderate (on average 41%; extremes 10-79%). The nonvolatile tris(2- methoxymethoxyphenyl)phosphine oxide by-product can be readily isolated and reduced to recover the phosphane starting material, or it may be hydrolyzed to the water-soluble tris(2-hydroxyphenyl)phosphine oxide.

The reaction of α-tert-butyldiphenylsilyl carbonyl compounds with organometallics leads with a high diastereoselectivity to erythro-β-hydroxysilanes, which under acidic or basic elimination conditions give E or Z di- and trisubstituted alkenes.

The lithium α-(dimethylamino)alkoxides resulting from the nucleophilic addition of an organolithium reagent to N,N-dimethylformamide are basic enough to deprotonate alkyltriphenylphosphonium salts suspended in tetrahydrofuran. The aldehydes liberated by t

Making use of the VB method of Malrieu et al. a force field has been developed, which allows to calculate heats of formation of hydrocarbons (conjugated and non-conjugated olefins, radicals and diradicals) with high accuracy.With this method radical stabilization energies (RSE) for a great number of delocalized radicals are calculated and compared with experimental values, derived from shock-tube measurements of dissociation energies or from rotational barriers of substituted olefins.A detailed analysis of the RSE with respect to structure, substituents, strain, and aromaticity is presented. - Key Words: Resonance energy / Heats of formation / Single pulse shock tube / Intrisic rotational barrier

Palladium-catalyzed cross-coupling of organic halides with organotin compounds in the presence of norbornadiene gave 5,6-disubstituted norbornene, which was treated by a retro Diels-Alder reaction yielding cis-ethene and cyclopentadiene.

(E,E) conjugated aromatic dienes can be efficiently prepared from aromatic halides and 1,3-dienes with high chemo, regio and stereoselectivities. Key words: Palladium; arylation; dienes; silver(I) salt; thallium(I) salt; (E,E) conjugated dienic aromatics.

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titanium reagent generated easily from allyldiphenylphosphine condenses with aldehydes to give (Z)-1,3-alkadienes in a highly regio- and stereoselective manner.In contrast, lithiated allyldiphenylphosphine oxide condenses with aldehydes to give (E)-1,3-alkadienes directly and stereoselectively in good yield.Similarly, lithiated (1-buten-3-yl)diphenylphosphine oxide condenses with aldehydes to give (E)-3-methyl-1,3-alkadienes.

A practical method for the stereoselective preparation of 1,3-dienes by the use of allyltriphenylsilane as a key reagent is described.

2-Allylic-substituted isoureas underwent Wittig-type allylidenation of aldehydes in the presence of triphenylphosphine and 2 molpercent of to give the corresponding conjugated olefins in tolerable to good yields.

The regiochemistry in reactions of heterosubstituted allylic carbanions (1) is highly controlled via allylic aluminum or boron "ate" complexes which direct both carbonyl compounds and reactive halides to the α-position with high regioselectivity.For example, carbonyl compounds react with the oxygen- (3), sulfur- (12), selenium- (20), and silicon- (25) substituted allylic carbanions at the α-position via the ate complexes.Although the reactions of the ate complexes (2) with aldehydes generally produce a mixture of erythro and threo isomers, the aluminum ate comlex of 3b gives the erythro isomer (5) with very high stereoselectivity.This procedure is applied to the stereoselective synthesis of exo-brevicomin (9).With allylic halides, the oxygen- (3a) and sulfur- (12) substituted allylic carbanions again react at the α-position via the ate complexes.However, the coupling mode is entirely different; the α-α' coupling product (10) is obtained from 3a, while the α-γ' coupling product (15) is produced from 12.

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New synthetic methods for the preparation of Z- or E-1,3-dienes are described.

Under gas-liquid phase-transfer catalysis conditions, an aldehyde passed in the gaseous state through a solid bed of potassium carbonate and a phosphonium salt, results in the formation of an alkene which is obtained in good yield by condensation and is free from triphenylphosphine oxide, which remains adsorbed on the bed.

Dimethylformamide dimethylacetal (2a) converts the threo-3-hydroxycarboxylic acids 4 smoothly into the (E)/(Z)-olefins 7/6 only if R2 is an aryl or vinyl substituent.Althougt the reaction exhibits a distinct (E)-selectivity it cannot be considered as a stereo-controlled olefin synthesis.If R2 is alkyl, 2a generates the methyl esters 10 from 4.The erythro-acids 5 react with 2a to give 43 - 95percent of >98percent sterically pure 7.As the key tranformation on the multistep way from 4/5 to 6/7 the fragmentation of the zwitterionic intermediate 11/20 is postulated.

ν3-Trimethylsilylallyltitanium compound, (ν5-C5H5)2Ti(ν3-1-trimethylsilylallyl), reacts with aldehydes to give (+/-)-(R,S)-3-trimethylsilyl-4-hydroxy-1-alkenes in excellent yields, which can be deoxysilylated to either E- or Z-1,3-dienes.

Dilithium carboxylic acid dianions 1 attack α,β-unsaturated aldehydes (2) 1,2-regiospecifically with formation of the unsaturated β-hydroxy carboxylic acids 3/4.Additionally, the addition of the phenylacetate dianion 1a can be conducted to the threo-isomer with high selectivity by reversible reaction. - α,β-Enones (8) add 1 irreversibly in 1,2- and 1,4-position.Depending on the substitution pattern, the whole range from pure 1,2- to pure 1,4-adduct is covered.The influence of the 1-counterion M and of the solvent is significant; the 1,4-portion increases with the complexing effect of M and with the Lewis-basicity of the solvent.

Pinacol E-1-trimethylsilyl-1-propene-3-boronate reacts with aldehydes to form (+)-(R*, S*)-3-trimethylsilyl-4-hydroxy-1-alkenes, which can be deoxysilylated stereoselectively to either 98percent Z or 99percent E 1,3-dienes, including the separate components of the red bollworm moth pheromone.

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