Trimethylenemethane reactions

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... 

B. M. Trost, S. A. King, and T. Schmidt, Palladium-catalyzed trimethylenemethane reaction to form methylenetetrahydrofurans. Aldehyde and ketone substrates and the tin effect, J. Am. Chem. Soc., Ill (1989) 5902-5915. 

Cycloaddition of COj with the dimethyl-substituted methylenecyclopropane 75 proceeds smoothly above 100 °C under pressure, yielding the five-membered ring lactone 76. The regiocheraistry of this reaction is different from that of above-mentioned diphenyl-substituted methylenecyclopropanes 66 and 67[61], This allylic lactone 76 is another source of trimethylenemethane when it is treated with Pd(0) catalyst coordinated by dppe in refluxing toluene to generate 77, and its reaction with aldehydes or ketones affords the 3-methylenetetrahy-drofuran derivative 78 as expected for this intermediate. Also, the lactone 76 reacts with a, /3-unsaturated carbonyl compounds. The reaction of coumarin (79) with 76 to give the chroman-2-one derivative 80 is an example[62]. 

Catalytic asymmetric Diels-Alder reactions are presented by Hayashi, who takes as the starting point the synthetically useful breakthrough in 1979 by Koga et al. The various chiral Lewis acids which can catalyze the reaction of different dieno-philes are presented. Closely related to the Diels-Alder reaction is the [3-1-2] carbo-cyclic cycloaddition of palladium trimethylenemethane with alkenes, discovered by Trost and Chan. In the second chapter Chan provides some brief background information about this class of cycloaddition reaction, but concentrates primarily on recent advances. The part of the book dealing with carbo-cycloaddition reactions is... 

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 [3+2] cycloaddition of trimethylenemethane (TMM) on the unsaturated lactam 288 worked efficiently with the use ofPd[P(0 Pr)3]4 (generated in situ from palladium(n) acetate (20mol%) and triisopropyl phosphite (160mol%)). The reaction proceeded cleanly in refluxing toluene to afford exclusively the desired cycloadduct 290 in 80% isolated yield (Equation 48) <2003TL5033>. 

Presumably the reaction takes place via the monoallene 225, which can be made the sole isomerization product if the rearrangement is carried out with sodium methoxide in methanol at 65 °C (yield 60%) [76], The intended intramolecular [2 + 2] cycloaddition to the diradical 227, a hybrid of trimethylenemethane and tetramethy-leneethane, could so far not be detected. 

Also to be mentioned are the reactions of oxygen atom radical anions with organic substrates. These reactions were reviewed by Gronert (2001). For the reactivity of the atomic oxygen anion-radical, see Section 1.7.2. The atomic oxygen anion-radical reacts with benzene, tetramethylene ethane, or cyclopentadienylidene trimethylenemethane. The reactions consist in abstraction of H2 with the formation of H2O and the corresponding distonic anion-radicals as products. 

In the same group, Feustel and G. Muller have observed an interesting reaction between two equivalents of the tris(phosphinomethyl)methanol 52 and five equivalents of n-butyl-lithium . Formally, the elimination of lithium oxide leads to the formation of a mixed aggregate of the lithium aUtoxide 53 and the dilithiated trimethylenemethane dianion 54 in the solid state (Scheme 19, Figure 15). The mechanism of the formal elimination of lithium oxide, which could also be part of a further mixed aggregate, has not been cleared up yet. 

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 addition of simple ester or ketoenolates to TT-allylpalladium complexes may constitute the second step of an ingenious [3 + 2] cycloaddition reaction. One substrate that undergoes this process is 2-(tri-methylsilylmethyl)allyl acetate (5). The mechanism proposed involves initial formation of a 2-(tri-methylsilylmethyl)allylpalladium cation followed by desilylation by the acetate liberated in the oxidative addition (Scheme 1). The dipolar intermediate can be envisioned as an T]3-trimethylenemethane-PdL2 species (6) or, less likely, an -complex (7). 

The addition of the trimethylenemethane-palladium complex to alkenes may proceed by a concerted process or via a stepwise mechanism in which the anion of the 1,3-dipole attacks Michael-fashion to generate an intermediate anion which collapses to form a five-membered ring by attack on the allylpalla-dium complex. This [3 + 2] cycloaddition reaction has been reviewed.128 A number of additional reports of its use have appeared recently.129-134... 

Reactions of mononuclear vinylidene complexes with other reactive metal complexes to give binuclear //-vinylidene complexes have been described above. Addition of Fe2(CO)c, to Mn(C=CHPh)(CO)2(i/-C5H5) also gives 31, by addition of a CO group to the a-carbon structural data are consistent with the delocalized formulation (31b), with its obvious resemblances to trimethylenemethane (60) ... 

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