Allenes to alkenes

The first step of this procedure illustrates a general reaction, the addition of allenes to alkenes to form methylenecyclobutanes. The reaction has been reviewed recently.7... 

Melhylenecydobutane-l,2-dicar-boxylic anhydride, 43,27 Methylenecydobutanes by addition of allenes to alkenes, 43, 30 Methylenecyclohexane, 40, 66 Methylene iodide, reaction with zinc-copper couple and cyclohexene, 41, 73... 

Cycloaddition of allenes to alkenes. This cycloaddition to give methylenecyclobutanes (3) can be realized in the presence of certain Lewis acids as catalysts (listed in approximate order of decreasing reactivity) C2H5AICI2, GaCls, AlBrj, AICI3, FeClj. 

Lewis acids, such as EtAlCL, GaCb and AlBrs, catalyze the cycloaddition of allenes to alkenes to give methylenecyclobutanes 151. 1-Alkenes and sterically hindered olefins, such as 4,4-dimethyl-2-pentene, do not react, and from butadiene only polymeric products are obtained. Substituted olefins react more readily, i.e. 1,1,2,2-tetraalkylethylene > 1,1,2-trialkylethylene > 1,2-dialkylethylene. The acid catalyzed [2+2] cycloaddition reaction most likely proceeds via a vinyl cation. The slightly exothermic reaction proceeds at room temperature in chlorobenzene and EtAlCb was used as a catalyst in the examples listed in Table 6.7... 

Catalysis of [2 + 2] Cycloadditions. EtAICI2 catalyzes a wide variety of [2 + 2] cycloadditions. These include the addition of alkynes or allenes to alkenes to give cyclobutenes and alkyli-denecyclobutanes (eq 14), the addition of electron-deficient alkenes to allenyl sulfides (eq 15), the addition of propiolate esters to monosubstituted and 1,2-disubstituted alkenes to form cyclobutene carboxylates (eq 16), and the addition of allenic esters to alkenes to form cyclobutanes. ... 

Secondary amines can be added to certain nonactivated alkenes if palladium(II) complexes are used as catalysts The complexation lowers the electron density of the double bond, facilitating nucleophilic attack. Markovnikov orientation is observed and the addition is anti An intramolecular addition to an alkyne unit in the presence of a palladium compound, generated a tetrahydropyridine, and a related addition to an allene is known.Amines add to allenes in the presence of a catalytic amount of CuBr " or palladium compounds.Molybdenum complexes have also been used in the addition of aniline to alkenes. Reduction of nitro compounds in the presence of rhodium catalysts, in the presence of alkenes, CO and H2, leads to an amine unit adding to the alkene moiety. An intramolecular addition of an amine unit to an alkene to form a pyrrolidine was reported using a lanthanide reagent. 

The groups R2N and Cl can be added directly to alkenes, allenes, conjugated dienes, and alkynes, by treatment with dialkyl-V-chloroamines and acids. " These are free-radical additions, with initial attack by the R2NH- radical ion. " N-Halo amides (RCONHX) add RCONH and X to double bonds under the influence of UV light or chromous chloride. " Amines add to allenes in the presence of a palladium catalyst. ... 

Nonstabilized carbonyl ylides (41) prepared by reaction of a-iodosilyl ethers with Smlj, can be trapped with various alkenes, alkynes and allenes to form furans of type 42, 43, and 44... 

The [(T -C3H5)PdCl]2/dppf/AcOH catalytic system has been used for the bis(hy-droamination) of 3-alken-l-ynes to alkenic 1,4-diamines (Eq. 4.94), a reaction which seems to be mechanistically related to the hydroamination of allenes since an a-al-lenic amine CH2=C=CH(R )CH2NR2 is believed to be an intermediate [318]. 

Although zirconium bisamides Cp2Zr(NHAr)2 do not catalyze the hydroamination of alkenes (see above), they are catalyst precursors for the hydroamination of the more reactive double bond of allenes to give the anti-Markovnikov addition product (Eq. 4.96) [126]. 

A typical second step after the insertion of CO into aryl or alkenyl-Pd(II) compounds is the addition to alkenes [148]. However, allenes can also be used (as shown in the following examples) where a it-allyl-r 3-Pd-complex is formed as an intermediate which undergoes a nucleophilic substitution. Thus, Alper and coworkers [148], as well as Grigg and coworkers [149], described a Pd-catalyzed transformation of o-iodophenols and o-iodoanilines with allenes in the presence of CO. Reaction of 6/1-310 or 6/1-311 with 6/1-312 in the presence of Pd° under a CO atmosphere (1 atm) led to the chromanones 6/1-314 and quinolones 6/1-315, respectively, via the Jt-allyl-r 3-Pd-complex 6/1-313 (Scheme 6/1.82). The enones obtained can be transformed by a Michael addition with amines, followed by reduction to give y-amino alcohols. Quinolones and chromanones are of interest due to their pronounced biological activity as antibacterials [150], antifungals [151] and neurotrophic factors [152]. 

Trost et al 2 briefly explored using non-enone enophiles. Simple alkenes led to the formation of complex mixtures of isomers due to the presence of an additional set of /3-hydrogens. Many other types of substrates were incompatible with reaction conditions. Vinyl ketones were, therefore, the only coupling partners shown to be effective in the ruthenium-catalyzed Alder-ene couplings of allenes and alkenes. 

In addition to alkenes and alkynes, allenes have attracted considerable interest due to their unique reactivity and multireaction sites. Therefore, transition-metal-catalyzed nucleophilic addition reaction of amines and imines to allenes has been extensively studied to prepare biologically important amines and nitrogen-heterocycles.31,31d... 

The cycloaddition of allenes to symmetrically disubstituted alkenes gives mixtures of cyclobutanes with stereochemical equilibration of the substituents. The reaction of 1,3-dimethylallenc with either diethyl fumarate or diethyl maleate produces a mixture of the /raw.v-bis(ethoxycar-bonyl)cyclobutanes.s The same nonstereoselectivity was observed for phenylallene and 1,1-dimelhylallene cycloadditions to maleic and fumaric acid diesters.9 10... 

The thermal reaction between two molecules of olefin to give cyclobutane derivatives (a 2 + 2 cycloaddition) can be carried out where the olefins are the same or different, but the reaction is not a general one for olefins.921 Dimerization of like olefins occurs with the following compounds F2C=CX2 (X = F or Cl) and certain other fluorinated alkenes (though not F2C=CH2), allenes (to give derivatives of 97),922 benzynes (to give biphenylene deriv-... 

---