Tetrahedrane synthesis

The tetrahedrane synthesis of Maier162) starting with 309 represents a clearcut [l,3,(4)2,(l)4]-elimination of carbon monoxide. The formation of 310 is an impressive example of the migration of two double bonds. 

Stereoselectivity. See Asymmetric induction Axial/equatorial-, Cis/trans-, Enantio-, Endo/exo- or Erythro/threo-Selectivity Inversion Retention definition (e.e.), 107 footnote Steric hindrance, overcoming of in acylations, 145 in aldol type reactions, 55-56 in corrin synthesis, 261-262 in Diels-Alder cyclizations, 86 in Michael type additions, 90 in oiefinations Barton olefination, 34-35 McMurry olefination, 41 Peterson olefination, 33 in syntheses of ce-hydrdoxy ketones, 52 Steric strain, due to bridges (Bredt s rule) effect on enolization, 276, 277, 296, 299 effect on f3-lactam stability, 311-315 —, due to crowding, release of in chlorophyll synthesis, 258-259 in metc-cyclophane rearrangement, 38, 338 in dodecahedrane synthesis, 336-337 in prismane synthesis, 330 in tetrahedrane synthesis, 330 —, due to small angles, release of, 79-80, 330-333, 337... 

The first genuine tetrahedrane synthesis was reported in 1978 by the Maier group the preparation of tetra-f-butyltetrahedrane, 5 [18]. This synthesis, which demanded astonishing persistence and experimental skill (the experimental details are reported in a 1981 paper [19]) is sketched here. 

Figure 25 Synthesis and structures of supersilyl-substituted gallanyls 396 and 400, gallanide 398 and tetrahedrane 401.

Also, there is an esthetic element mixed into this motivation, which probably is derived from the tradition of stripped-down test molecules in physical organic chemistry, in which studies of the parent member of a series tend to be valued more highly than those of its derivatives. One thinks, for example, of the emphasis placed on studies of the unsubstimted molecules methylene, norbomyl cation, cyclobutadiene, tetrahedrane, benzyne, and so on. The higher valuation also is associated in some cases with the formidable difficulties experienced by experimentalists in the synthesis and observation of these species. 

Next, some reactions of hexakis(trifluoromethyl)benzvalene will be discussed. This compound is very stable as mentioned before and its olefinic double bond reacts as an efficient dienophile. The difference in the reactivity between unsubstituted benzvalene and the hexakistrifluoromethylated derivative is that the former is nucleophilic while the latter is highly electrophilic. Thus, the former does not react with usual 1,3-dienes, in contrast to the latter. Here, mainly describe our results of the several reactions of hexakis(trifluoromethyl)benzvalene which were designed for the synthesis of tetrakis(trifluoromethyl)tetrahedrane. 

Despite the highly unusual structure of tetrahedrane, 3, the problem of its synthesis had been formulated more than 70 years ago (96). The first review article on tetrahedrane (97) appeared almost simultaneously with the paper describing the first synthesis of its tetra-t-butyl derivative 77 (5), which, until recently (98), remained the only tetrahedrane derivative known. On the basis of MM calculations using different force fields Hounshell and Mislow predicted T symmetry for 77 (99). Minkin etal. (17c) discussed the synthesis, reactions, and stability of 3 and 77 pointing out that high kinetic stability of the latter molecule is partly due to unfavorable steric repulsions in the... 

Vahrenkamp first synthesized the chiral tetrahedrane type clusters (270), which have been resolved for M = Mo via the diastereoisomeric phosphane (271), and a directed synthesis has achieved the construction of the /ij-S-bridged tetranuclear CoFeMoW cluster (272). 

A challenge to synthesis this is a consequence of the expected high strain in tetrahedrane. Novel reactions and extraordinary experimental skill are often needed to construct highly strained molecules. 

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