Methylene-trimethylenemethane

The [Pd(dba)2l-catalysed asymmetric 3+2-cycloaddition of methylene-trimethylenemethane with a, -unsaturated A/-acylpyrroles produced substituted... 

Versatile [3 + 2]-cydoaddition pathways to five-membered carbocydes involve the trimethylenemethane (= 2-methylene-propanediyl) synthon (B.M. Trost, 1986). Palladium(0)-induced 1,3-elimination at suitable reagents generates a reactive n -2-methylene-l,3-propa-nediyl complex which reacts highly diastereoselectively with electron-deficient olefins. The resulting methylenecyclopentanes are easily modified, e. g., by ozonolysis, hydroboration etc., and thus a large variety of interesting cyclopcntane derivatives is accessible. 

Draw resonance structures for the trimethylenemethane anion C(CH,) 2 in which a central carbon atom is attached to thi ee CH, groups (CH, groups are referred to as methylene). 

The third member, trimethylenemethane (3), had some relevance to our studies on carbenes, since besides methylene and its simply substituted derivatives trimethylenemethane 3 is one of the few molecules having a triplet ground state.22 Also the experience with 3 could be of help in order to deal with the singlet/triplet differentiation in matrix-isolated carbenes. We learned that, if the calculated IR spectra of the singlet and triplet molecule are sufficiently different, it might be possible to determine the multiplicity of the matrix-isolated species by comparison with the experimental IR spectrum. In this context it is also worth mentioning that we were able to measure the matrix IR spectrum of 3, but a special technique (irradiation in halogen-doped xenon matrices) had to be developed in order to achieve a concentration of 3 sufficient for its IR detection.23... 

Diradicals represent the most clear-cut application of the SF approach because in these systems the non-d namical correlation derives from a single HOMO-LUMO pair (e.g., n and n in twisted ethylene). In this section we present results for methylene and trimethylenemethane (TMM). 

Methylenecyclopentanes.2 Trost and Curran have used 1 as an electrophilic synthon for trimethylenemethane. Thus 1 reacts with the anion of 2 to give 3 in 72% yield. This product was oxidized to the disulfone, which was then cyclized to 4 by F. Various transformations are possible for the exocyclic methylene group. For the synthesis of coriolin (6), the group was converted to a pem-dimethyl group by cyclopropanation and hydrogenolysis. The product (5) was converted in several more steps into 6. 

Write down the simple Hiickel Fock matrices (in each case using a, (3 and 0, and 0,-1 and 0) for (1) the pentadienyl radical (2) the cyclopentadienyl radical (3) trimethylenemethane, C(CH2)3 (4) trimethylenecyclopropane (5) 3-methylene-l, 4-pentadiene. 

Ground-state triplet dicarbenes in photochemical systems have also been extensively studied by ESR. Dowd and coworkers (304) examined the interesting, frequently postulated ground triplet trimethylenemethane obtained by photolysis of either 4-methylene-A -pyrazoline or a single crystal of 3-methylene-cyclobutanone. This triplet molecule is axially symmetrical and the proton hyperfine splittings of 8.9 gauss observed in single-crystal experiments indicate that all protons in the molecule are equivalent when the axis perpendicular to the plane... 

From methylene(vinyl)cyclopropane, XLV, the vinyl-substituted trimethylenemethane, XLVI, is obtained (43%) ... 

In 1932 Kon and Naji reported that pyrolysis of trans-2,3-ethoxycarbonyl-methylenecyclopropane ( Feist s ester ) resulted in an isomerization to give compounds later identified as the stereoisomeric 2-carbethoxy-l-(carbethoxy-methylene)cyclopropanes (Figure 36). Subsequent studies by Ullman " using the optically resolved reactant showed that the products were not racemic and that the planar trimethylenemethane biradical could not, therefore, be the sole intermediate in the... 

As the proceeding chapters demonstrate, Ni(0)- and Pd(0)-catalyzed [3-1-21-cycloadditions of methylenecyclopropanes with alkenes open a new, simple, and useful route to a number of substituted methylenecyclopentanes. This catalytic generation of a trimethylenemethane synthon and its addition to olefinic double bonds not only lead to five-membered rings but also introduce an exocyclic methylene group, which is a useful functionality for further structural elaboration. 

A number of investigations have appeared documenting the metal-mediated cleavage of a variety of cyclopropane derivatives, particularly those which are more reactive than ordinary cyclopropanes due to additional structural strain, unsaturation and/or substituents. In a pioneering study, methylene cyclopropane was shown to react with Fe2(CO)9 to furnish trimethylenemethane complex 6 [15]. 

For example, the singlet trimethylenemethane 6.365 can be produced by heating the strained bicyclic hydrocarbon 6.363 or the diazene 6.364, or by photolysis of the latter. It dimerises to give a mixture of at least three hydrocarbons out of the eight possible, of which one stereoisomer of the fused-bridged product 6.366 is the major. The exocyclic methylene carbon is the unique carbon, and can be assigned to be the one with the large coefficient in ip2 and a zero coefficient in The experimental result can then be explained if the former is the HOMO and the latter the LUMO.873... 

Methylenecyclopropane in the free state may also be regarded as trimethylenemethane (Scheme 11,4A), but on chemisorption the former structure is the more appropriate because with this compound hydrogenation gives simultaneously methylcyclopropane and butanes in which then-isomcrpredominates. Breaking at the C—C bond opposite the point of substitution also occurs with ethenylcyclopropanes, and prior chemisorption at the C=C bond facilitates the splitting of the nearer C—C bond. However the insertion of a methylene group... 

---