Octaplane

C(C)4 have been found... 35 Two years later, Rasmussen and Radom30 designed the first stable ptC surrounded only by carbons, [ptC(C)4], the dimethanospiro[2,2]octaplane (Figure 3).30 Wang and Schleyer found a set of boron spiroalkanes with a ptC(C)4 through substitution of carbon by boron atoms.36,37 In 2003, a novel family of molecules based on a C( moiety was proposed by us, which constituted the simplest and smaller set of molecules containing a ptC(C)4, and more importantly, the first and, at that time, the only one stabilized purely by electronic factors.38... 

To return now to the examination of octaplane and its more-constrained siblings. The optimized HF/6-3 lG(d) stmcture of octaplane (the PES minimum) has a CCC angle of 169°, approaching the 180° an e of planar caibon (the tetralre-dral angle is of course 109.5°). However, the central carbon of this S4 stmctiue showed considerable reluctance to flatten to planarity (C4h), as revealed by an... 

Fig. 1.6 Dimethanospiro[2.2] octaplane, 4. This is the calculated structure at the MP/6-31G(d) level...

This study of dimethanospiro[2.2]octaplane must leave tittle doubt that its central carbon is either perfectly planar, or that the barrier to planarization is very small, in which latter case the relative-minimum species probably has a nearly-planar central carbon (one longs for the day when computer power will permit a CCSD(T) [37,38] optimization/frequency calculation with a 6-31G(d) or bigger basis on a molecule like this). Radom and Rasmussen followed this discovery of the very promising... 

Fig. 1.7 Molecules 5 and 6 are closely related to dimethanospiro[2.2]octaplane but perhaps easier to synthesize 5 resembles closely the well-known pagodane, 7...

Fig. 1.10 The cyclopropylidene and the allene from opening of the spiropentane moiety ofdime-thanospiro[2.2]octaplane. These are molecular mechanics structures. The cyclopropylidene structure shown here actually has the carbons of the three-membered ring and the two carbons of the double bond in the same positions as the corresponding carbons of the spiropentane moiety of dimethanospiro[2.2]octaplane, and so its function here is only heuristic (cf. Fig. 1.9)...

The most likely abode that has been devised for a planar carbon atom, dimethano-spiro[2.2]octaplane (4), poses a formidable synthetic challenge by virtue ( ) of its... 

Fig. 1.12 An elaboration on the concept shown in Fig. 1.11. Retrosynthetic analysis of dimeth-anospiro[2.2]octaplane (4) leads here to 10, and then to 11, which is depicted more realistically as 12, with a tetrahedral, rather than a planar, central carbon. The carbonyl groups shown are only suggestive of the synthetic handles that might be used to manipulate carbon-carbon bondmaking...

A series of computer experiments by Radom and Rasmussen iderrtified prorrrising candidates for perfectly-planar-carbon molectrles, the most prorrrising of which were dimethanospiro[2.2]octaplane arrd dimethanospiro[2.2]binorraplane. Becanse of their size, complexity, and the strain inctrrred by planar carborr, these compotrrtds represent formidable synthetic challenges nevertheless, it is conceivable that they could yield to a thorough retrosynthetic analysis followed by skillful implementation of one of the thus-revealed putative routes. 

---