Trimethylenemethane complexes reactions

Scheme 21. The gas-phrase reactions of CoO+ with 2-methylpropane (iso-butane). Note that the compound labeled A is a 2-methyl-l-propene (iso-butylene) complex of Co , while the compound labeled B is a trimethylenemethane complex of Co. ...

The reaction of methylenecyclopropanes with transition metal complexes is well known to promote a catalytic a-ir cycloaddition reaction with unsaturated compounds, in which a trimethylenemethane complex might exist71-76. Recently, much interest has been focused on the interaction of strained silicon-carbon bonds with transition metal complexes. In particular, the reaction of siliranes with acetylene in the presence of transition metal catalysts was extensively investigated by Seyferth s and Ishikawa s groups77-79. In the course of our studies on alkylidenesilirane, we found that palladium catalyzed reaction of Z-79 and E-79 with unsaturated compounds displayed ring expansion reaction modes that depend on the (Z) and (E) regiochemistry of 79 as well as the... 

In trimethylenemethane complexes, the metal stabilizes an unusual and highly reactive ligand which cannot be obtained in free form. Trimethylenemethanetricar-bonyliron (R=H) was the first complex of this kind described in 1966 by Emerson and coworkers (Figure 1.2) [38]. It can be obtained by reaction of bromomethallyl alcohol with Fe(CO)5. Trimethylenemethaneiron complexes have been applied for [3+2]-cycloaddition reactions with alkenes [39]. 

In a variation on the two-component cycloaddition reaction, a [3+3] strategy was reported whereby reaction of enantiomerically pure aziridines, generated from amino acids, with palladium trimethylenemethane complexes leads to a piperidine (Scheme 114). Yields ranged from 63% to 82% and the efficiency of the methodology was demonstrated by the four-step synthesis of (—)-pseudoconhydrin <2001SL1596>. 

First, cis- and trans-2-phenylmethylenecyclopropanes-3-d were shown to give trimethyl-enemethane complexes with the deuterium at a location consistent only with disrotatory ring-opening (Figure 41). Second, reaction of 2,2-diphenylmethylenecyclopropane with a variety of iron carbonyl reagents allowed isolation of the methylenecyclopropane iron tetracarbonyl complex. This compound could be shown to give the trimethylenemethane complex on reaction with trimethylamine-N-oxide or diiron nonacarbonyl, both of which... 

JOM(322)103>. Other more exotic addition reactions of (55) have also appeared including reactions with allenes <90OM289> and phosphinimines <89JA7279,920M2613). The former reaction is an efficient method for the preparation of iron trimethylenemethane complexes. 

Interestingly, attempts to use the bis-allylic alcohol as the substrate in the analogous reaction led to isolation of the ferrilactone complex (61) as the major product, accompanied by a trace of the trimethylenemethane complex. Conversely, reaction in THF at room temperature resulted in a complete reversal of the product distribution [256] (Scheme 136). The reasons for this are currently unclear. 

Scheme 4.30 summarizes the proposed reaction mechanism. The substrate would react with palladium(O) species to form a palladacyclobutane intermediate A in equilibrium with the tautomeric trimethylenemethane complex A. Insertion of CO2 into the palladium-carbon bond affords a palladium carboxylate, which can release y-lactone 27 by reductive elimination. The latter species can isomerize to the thermodynamically more stable furanone 28. a,p-Unsaturated lactone 28 contains acidic protons and, in principle, can react with intermediates A and/or A (Scheme 4.30) to give cooligomers, which have been observed as by-products. 

The reactions of various iron carbonyl complexes, such as Fe(GO)4(NMe3), with allene compounds under photo-lytic conditions, yield chelated 77 -allyliron complexes. Two brief reviews discussing the chemistry and application to organic synthesis of these (7r-allyl)tricarbonyl iron lactone complexes have appeared recently. Reaction of the iron lactone complexes with trimethyloxonium tetrafluoroborate yields the carbene complex 23 in good yields. Treatment of the cationic carbene complex with triphenylphosphine results in substitution at the terminal end of the allyl ligand of the trimethylenemethane complex 24. 

A short time after the first synthesis of a trimethylenemethane complex, Noyori et al. reported a new access to the class of compounds starting from methylenecyclopropane derivatives. While treatment of methylenecyclopropane with diironenneacarbonyl afforded 3 only in very poor yield in addition to (l,3-butadiene)tricarbonyliron, substituted systems such as 2-methyl-2-phenylmethylenecyclopropane (4) gave trimethylenemethane complexes such as 5 in up to 60% yield (Scheme 10.2) [14]. These results reflect the tendency of strained small rings to undergo ring-opening reactions in the presence of transition metal complexes. However, few stable complexes of methylenecyclopropane have been described [15]. 

In addition to dihalides such as 2, other organohalides can serve as precursors for the synthesis of trimethylenemethane complexes by dehalogenation. This dehalogenation can be afforded not only by iron carbonyls but also by disodium tetracarbonylferrate(-II). For example, the reaction of 2-(bromomethyl)allyliron halide 6 with Fe2(CO)g afforded trimethylenemethane complex 3 in 91% yield (Scheme 10.3) [16]. 

Another general way to prepare trimethylenemethane complexes is the reaction of trimethylenmethane dianions with metal halides. By this way. Mills et al. obtained (cyclopentadienyl)(trimethylenemethane)cobalt (21) in 18% yield by dilithiation of isobutene (19) with butyllithium/tetramethylethylenediamine (TMEDA) to dianion 20 [22,23] followed by treatment with 1 equiv. of (cyclopen-tadienyl)diiodo(triphenylphosphane)cobalt (Scheme 10.7). The crystal structure analysis shows a highly symmetric molecule with a slight pyramidalization of the trimethylenemethane ligand away from the cyclopentadienylcobalt... 

More specialized approaches include the reaction of allene (24) with the methylidene iridium complex 25 at -80 C, which gave trimethylenemethane complex 26 in 80% yield (Scheme 10.9) [27]. 

The reactivity of trimethylenemethane complexes has not been studied extensively. There are, however, a number of catalytic reactions, for which the intermediacy of trimethylenemethane complexes is plausible albeit not proved in all cases, stepwise processes might also be considered [33]. The most prominent examples in this context are palladium-catalyzed trimethylenemethane cycloadditions [34,35] in the presence of a phosphane or phosphite, starting from 2-acetoxymethyl-3-allyltrimethsilane (33), which have been explored in great depth by Trost et al. [36, 37]. 33 undergoes [3-1-2]- as well as [3-H4]cyclizations with electron-poor alkenes or dienes such as 34, respectively, leading to 35 and 36 (Scheme 10.13). 

Palladium-catalyzed intramolecular [3+2] cycloadditions starting from alkenylidenecyclopropanes have been reported by Mascarenas et al. [44]. For related nickel-catalyzed reactions, the intermediacy of trimethylenemethane complexes has not been invoked [45]. 

In another reaction of a trimethylenemethane complex, Sita et al. identified the unanticipated nucleophilic reactivity of the hgand in an electroneutral zir-conium(IV) complex 41. Nucleophihc addition of methyl, ethyl, or trimethylsilyl triflate, benzyl bromie, or trimethylsilyl chloride afforded adducts 42 in 50-98% yield (Scheme 10.15). The authors rationahzed the unexpected behavior on the basis of density functional theory (DFT) calculations [46]. 

In a similar way, the reaction of carbinol 96 with diironenneacarbonyl afforded heptafulvene complex 97 in 48% yield, showing a trimethylenemethane complex substructure. Further reaction with the iron reagent gave dinuclear complex 98 in 77% yield (Scheme 10.33). The products were characterized by IR, MS, and... 

Cyclic Dienes. Ring opening of cis- and rrfl/is-2-phenylmethylene[3- Hi]-cyclopropane yields stereospecifically the trimethylenemethane complexes (82a, b), respectively the results are consistent with an allowed disrotatory ring opening, and are in agreement with frontier MO calculations. The exo-complex (83) and its enrfo-isomer have been prepared by reaction of the free... 

Trimethylenemethane complexes have been first described by Emerson et al. by reaction of 3-chloro-2-(chloromethyl)propene with nonacarbonyldiiron. The reaction can also be smoothly carried out under ultrasonic conditions at room temperature to give a high yield of 90% (Scheme 4-84). ... 

Trimethylenemethane is a special type of alkene that does not exist as the free compound. Various synthetic equivalents to the synthon 43 shown below have been reported. Trost, in particular, has exploited these compounds in 1,3-dipolar cycloaddition reactions.138 139 A metal-bound, isolated trimethylenemethane species was recently reported by Ando (Scheme 6). It resulted from the complexation of an ero-methylenesila-cyclopropene with group 8 carbonyls (Fe, Ru).140,140a The structure was proved by X-ray crystal structure analysis.29Si NMR data were consistent with the -structure shown. 

The palladium-catalyzed hetero-[4 + 3]-cycloadditions reported by Trost and Marrs utilize a metal-complexed trimethylenemethane as the three-carbon component. These complexes react with a,/3-unsaturated imines to produce seven-membered heterocycles in moderate to good yields.84 Two examples of this reaction were reported and are shown in Equations (13) and (14). Only the [4 + 3]-reaction was observed with a,/3-unsaturated imine 76 however, both the [4 + 3]- and the [3 + 2]-modes of reactivity are observed with a,/3-unsaturated imine 79. 

The palladium-catalyzed trimethylenemethane reaction with tropanones was reported in 1987 by Trost and Seoane and is the first example of a [6 + 3]-cycloaddition.130 Chromium-mediated [6 + 3]-cycloadditions of two types have been described-one in which the chromium complex activates the six-carbon component and one in which the chromium complex activates the three-atom component. An example of the first type involves the reaction of a cycloheptatriene-Cr(CO)3 complex with azirines to give cyclic imines in moderate yields (Scheme 40).131... 

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