Trimethylenemethane TMM

Cycloaddition involving the Pd-catalyzed trimethylenemethane (TMM) fragment 63 and the 1.3-diene 61 with an EWG offers a good synthetic method for the hydroazulene skeleton 65. The cydoaddition of trimethylene-... 

The discovery of palladium trimethylenemethane (TMM) cycloadditions by Trost and Chan over two decades ago constitutes one of the significant advancements in ring-construction methodology [1]. In their seminal work it was shown that in the presence of a palladium(O) catalyst, 2-[(trimethylsilyl)methyl]-2-propen-l-yl acetate (1) generates a TMM-Pd intermediate (2) that serves as the all-carbon 1,3-di-pole. It was further demonstrated that (2) could be efficiently trapped by an electron-deficient olefin to give a methylenecyclopentane via a [3-1-2] cycloaddition (Eq. 1). 

The (pentamethylcyclopentadienyl)zirconium amidinate unit also served as a platform for the synthesis and characterization of remarkable cationic and zwitterionic allyl zirconium complexes derived from trimethylenemethane (TMM). A direct synthetic route to the neutral precursors was found in the... 

Interactions polarize bonds. Trimethylenemethane (TMM) and 2-buten-l,4-diyl (BD) dianions (Scheme 6a, b) are chosen as models for hnear and cross-conjngated dianions. The bond polarization (Scheme 7) is shown to contain cyclic orbital interaction (Scheme 6c) even in non-cyclic conjugation [15]. The orbital phase continnity-discon-tinnity properties (Scheme 6d, e) control the relative thermodynamic stabihties. 

There is a degree in the continuity and discontinuity of the orbital phase [20]. 2-Oxopropane-l,3-diyl (Scheme 10) is a hetero analog of trimethylenemethane (TMM) where the orbital phase is continuous in the triplet diradical (Sect. 2.1.5) and discontinuous in the singlet diradical (Sect. 2.1.6). The n and orbitals of carbonyl bonds are lower in energy than those of C=C bonds. The lowering strengthens the interaction of the radical orbitals (a, b) with and weakens that... 

The well-established prototypes of 1,3-diradicals, trimethylenemethane (TMM, 1) and trimethylene (TM, 2) are selected to illustrate our idea. The diradical is assumed to have two singly occupied orbitals, p and q, of nearly the same energy on two radical centers (P and Q in Fig. 4). As addressed in Sect. 2, it is possible for... 

The Franck-Condon question is also an issue in diradical studies. It is particularly relevant in nonrigid systems, such as trimethylenemethane (TMM) and tetramethyleneethylene (TME), °° in which neutral and/or anion states can be planar or nonplanar. Thus, transitions can occur from planar anions to nonplanar neutral states, or from nonplanar anions to planar neutrals. In these cases, the energy differences between the planar and nonplanar states have generally been estimated by using quality electronic structure calculations. 

Construction of the cyclopentane ring was accomplished by utilization of Trosf s Pd-mediated diastereoselective [3+2] trimethylenemethane (TMM) cycloaddition [4] on the cinnamate 5 having an Evans type chiral auxiliary [4b], The resulting diastereomeric mixture (3 1 at best) of 7a and 7b was separated by careful silica gel column chromatography (7a is less polar than 7b under normal phase). Puri-... 

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>. 

One such typical transformation is the thermal isomerization of the spiropentane derivative 76 into triene 80 which is assumed to occur via the diene intermediate 78 with the intermediate participation of the cyclopropyl-trimethylenemethane (TMM) 77 and the vinyl-TMM 79 diradicals (equation 29)44. It was shown by using deuterium labels that the diradical 79 forms the triene 80 by 1,6-hydrogen shift. The pathway 76 — 80 which occurs via tetramethylene-ethane diradical was recognized as a less probable route. 

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). 

Stable five-membered ring adducts of Cgg can be synthesized by ]3+2] cycloadditions of trimethylenemethanes (TMM) [13, 195], The TMM intermediates are prepared in situ by thermolysis of 7-alkylidene-2,3-diazabicycloheptene (non-polar TMM) or methylenecyclopropanone ketals (polar TMM). With the mefhylenecyclopropanone ketal addition (Scheme 4.31), 185 and 186 were isolated after chromatography on silica gel. 

An example is trimethylenemethane (TMM), one of the first hydrocarbon biradicals whose triplet ESR spectrum was recorded (cf. Chapter 5 in this volume), but which eluded 25 years of efforts (among others by the present author) to obtain its UV-vis or IR spectrum, because the predominant product of photolysis or pyrolysis of different precursors was invariably methylenecyclopropane (MCP). Eventually, Maier et al. successfully generated a sufficient quantity of TMM, by irradiation of MCP in halogen-atom doped Xe matrices, to record the IR spectrum of this elusive compound. 

From a mechanistic point of view (see below) it is important to note that the chloropalladation of labeled 2,2-diphenyl-l-methylenecyclopropane-3,3-d2 gave only two isomeric complexes, with absence of the isomer in which both the phenyl and deuterium reside on the allylic moiety (equation 323). This allows the exclusion of a symmetrically bound >/4-trimethylenemethane (TMM) intermediate or rapidly equilibrating >/3-TMM species,... 

The synthesis of organic metals containing either a tetrathiafulvalene (TTF) system255 or a trimethylenemethane (TMM) system256 (equation 26) has been accomplished by thionation with P4S10. 

Free trimethylenemethane (TMM) is also a highly reactive species. It has no Kekule resonance form and can only be observed by trapping at low temperatures in a neutral... 

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