Trans-disubstituted Alkenes Research Articles

Organoselenium-Catalyzed Enantioselective Synthesis of 2-Oxazolidinones from Alkenes.

An operationally simple method for generating enantioenriched 2-oxazolidinones from N-Boc amines and mono- or trans-disubstituted alkenes via chiral organoselenium catalysis is described. Critical to the success of the transformation was the inclusion of triisopropylsilyl chloride (TIPSCl), likely because it sequestered fluoride generated by the oxidant (N-fluorocollidinium tetrafluoroborate) throughout the reaction and suppressed side reactivity. The scope of both the amine and alkene substrates was explored, generating a variety of 2-oxazolidinones in modest to high yields with high enantioselectivities.

Nickel-catalysed cycloaddition oligomerisation of 1,6-diynes to medium-size cyclic polyenes

A nickel-catalysed reaction of 1,6-diynes produced cyclic polyene oligomers with a narrow PDI. Their thermal isomerization gave the regio-isomeric cyclic polyenes consisting of trans-disubstituted alkenes.

Catalytic Oxygenative Allylic Transposition of Alkenes into Enones with an Azaadamantane-Type Oxoammonium Salt Catalyst.

The first catalytic oxygenative allylic transposition of unactivated alkenes into enones has been developed using an oxoammonium salt as the catalyst. This reaction converts various tri- and trans-disubstituted alkenes into their corresponding enones with transposition of their double bonds at ambient temperature in good yields. The use of a less-hindered azaadamantane-type oxoammonium salt as the catalyst and a combination of two distinct stoichiometric oxidants, namely, iodobenzene diacetate and magnesium monoperoxyphthalate hexahydrate (MMPP⋅6 H2 O) are essential to facilitate the enone formation efficiently.

Synthesis of trans‐Disubstituted Alkenes by Cobalt‐Catalyzed Reductive Coupling of Terminal Alkynes with Activated Alkenes

A cobalt-catalyzed reductive coupling of terminal alkynes, RC≡CH, with activated alkenes, R'CH=CH(2), in the presence of zinc and water to give functionalized trans-disubstituted alkenes, RCH=CHCH(2)CH(2)R', is described. A variety of aromatic terminal alkynes underwent reductive coupling with activated alkenes including enones, acrylates, acrylonitrile, and vinyl sulfones in the presence of a CoCl(2)/P(OMe)(3)/Zn catalyst system to afford 1,2-trans-disubstituted alkenes with high regio- and stereoselectivity. Similarly, aliphatic terminal alkynes also efficiently participated in the coupling reaction with acrylates, enones, and vinyl sulfone, in the presence of the CoCl(2)/P(OPh)(3)/Zn system providing a mixture of 1,2-trans- and 1,1-disubstituted functionalized terminal alkene products in high yields. The scope of the reaction was also extended by the coupling of 1,3-enynes and acetylene gas with alkenes. Furthermore, a phosphine-free cobalt-catalyzed reductive coupling of terminal alkynes with enones, affording 1,2-trans-disubstituted alkenes as the major products in a high regioisomeric ratio, is demonstrated. In the reactions, less expensive and air-stable cobalt complexes, a mild reducing agent (Zn) and a simple hydrogen source (water) were used. A possible reaction mechanism involving a cobaltacyclopentene as the key intermediate is proposed.

Regioselective Nickel‐Catalyzed Reductive Couplings of Enones and Allenes

Catalytic reductive coupling processes have been developed in numerous contexts as a strategy for the regioand stereoselective installation of alkenes. The direct coupling of a polar p system with a relatively nonpolar p system is often a successful strategy for selectively accomplishing synthetically desirable heterocouplings while avoiding undesired homocoupling of either reagent. For example, reductive couplings of aldehydes, enones, enals, or imines paired with alkynes, alkenes, or allenes have been extensively developed in recent years. Processes of this type are often highly effective in controlling both the position and stereochemistry of di-, tri-, and tetrasubstituted alkenes within polyfunctional molecules. Among these methods, the preparation of g,dunsaturated carbonyl groups by nickeland cobalt-catalyzed processes has been the subject of considerable study. The catalytic strategies developed for synthesis of g,d-unsaturated carbonyl groups by the coupling of two p-containing components include enone–alkyne additions in work reported by our group and by Cheng and co-workers, and enone–alkene additions in work reported by Jamison and co-workers, and Ogoshi et al. (Scheme 1). Processes of this type provide an important counterpart to organocuprate technology and hydrometallative processes, while having the advantage of not requiring the stoichiometric preparation of an alkenyl metal species. Stereodefined trisubstituted alkenes 1, trans-disubstituted alkenes 2, and monosubstituted alkenes 3 may be readily prepared by the above-mentioned enone–alkyne and enone– alkene coupling processes. However, a general strategy for the preparation of 1,1-disubstituted alkenes 4 by these methods has not been developed. Since terminal alkyne reductive coupling strategies and hydrometallative processes typically favor formation of the conjugate addition product 2 with a 1,2-disubstituted alkene, the 1,1-disubstituted alkene 4 is considerably more difficult to prepare. As depicted below (Scheme 2), regiocontrolled reductive coupling of an

Syn-Diacetoxylation of Alkenes with Palladium and Molecular Oxygen

While various palladium-catalyzed methods for alkene difunctionalization have appeared recently in the literature, most of these protocols require the use of PhI(OAc)2 as oxidant to oxidize Pd(II) to Pd(IV). In the present study the authors report the first example of a palladium-catalyzed diacetoxylation of alkenes using direct oxygen-mediated Pd(II)/Pd(IV) oxidation. An array of cis- and trans-disubstituted alkenes is efficiently diacetylated to provide syn products in high yields and diastereoselectivities.

Efficient epoxidation of alkenes with aqueous hydrogen peroxide catalyzed by methyltrioxorhenium and 3-cyanopyridine.

The epoxidation of alkenes with 30% aqueous hydrogen peroxide is catalyzed efficiently by methyltrioxorhenium (MTO) in the presence of pyridine additives. The addition of 1-10 mol % of 3-cyanopyridine increases the system's efficiency for terminal and trans-disubstituted alkenes resulting in high isolated yields of the corresponding epoxides. The system allows for epoxidation of alkenes with various functional groups. Alkenes leading to acid-sensitive products are efficiently epoxidized using a mixture of pyridine and 3-cyanopyridine as additives. This method is operationally very simple and uses an environmentally benign oxidant. The effects of different pyridine additives on the alkene conversion and the catalyst lifetime are discussed.

Enantioselective epoxidation of trans-disubstituted alkenes by D2-symmetric chiral dioxoruthenium(VI) porphyrins

A series of D2-symmetric chiral trans-dioxoruthenium(VI) porphyrins can effect enantioselective epoxidation of trans-β-methylstyrene in up to 70% ee, and 76% ee is attained for the oxidation of cinnamyl chloride; the facial selection for the trans-alkenes epoxidation is explained by a ‘head-on approach’ model.

Diastereofacial Selection in Nitrile Oxide Cycloaddition Reactions. The Anti-Directing Effect of an Allylic Oxygen and Some New Results on the Ring Metalation of Isoxazolines. A Synthesis of (±)-Blastmycinone.

The extent of diastereoselectivity associated with the reactions of nitrile oxides with alkenes bearing an allylic oxygen substituent has been studied. Reasonable levels of such diastereoselectivity have been found when the tert-butyldimethylsilyl ether derivative of 3-buten-2-ol (5) or (+)-(S)-isopropylidene-3-butene-1,2-diol (1) are employed as dipolarophiles. The stereochemical course of these cycloaddition reactions has been proven rigorously through the transformation of the adducts to known γ-lactones. The stereochemistry associated with the metalation/alkylation of 5-alkoxymethyl-substituted isoxazolines has also been probed in order to further expand the use of these heterocycles as aldol equivalents in natural products total synthesis. A synthesis of (±)-blastmycinone (34) is reported which combines the two foregoing aspects of stereocontrol. The levels of regio- and stereoselectivity found in the cycloaddition reactions of the cis- and trans-disubstituted alkenes 35 and 39 prepared from isopropylidene-D-glyceraldehyde are also discussed. A single example of the reaction of a chiral alkene with a chiral nitrile oxide is presented.

Dynamic behaviour of bis(DIOP)palladium and its reaction with alkenes

The dynamic behaviour of bis(DIOP)palladium is studied by complete line-shape analysis of its 31P NMR spectrum. Its reaction with trans-disubstituted alkenes gives diastereomeric complexes, the selectivity depending on the nature of the substituents.