Fenestranes structure

Photochemical [3 + 2] photocycloaddition of alkenes to benzene ring is a useful tool for construction of 5-membered ring compounds in a one-step. Penkett reported the synthesis of the [5.5.5.5] fenestrane structures (47), (48), (50) by arenyl-diene (either 46 or 49) double [3 + 2] photocycloaddition reactions. Penifulvins (53), natural products, were prepared by use of an intramolecular [3 + 2] photocycloaddition of (51) as a key step." ... 

Another example of geometrical consequences of intramolecular interactions can be demonstrated by the structure of a few carbon-cage molecules. Whereas the adamantane molecule [57] has only one kind of C-C distance, due to its high symmetry, there is a distribution of C-C distances in, for example, heptacy-clotetradecane (Figure 12(a)) [67] and fenestrane (Figure 12(b)) [68] due to intramolecular nonbonded interactions. 

The impetus to prepare a novel type of carbon framework, like that present in the structures 138a or 139, prompted intensive studies to elaborate new synthetic protocols. Examples illustrative of the strategy were shown earlier e.g. Sections 2.19.2 and 3.2.6), but the existing data are too scarce to discuss the specifics of the chemical reactivity of fenestranes arising from the planarization effects. 

The reactions shown in Scheme 4.49 imply an ease of formation for carbocationic intermediates with carbenium ion center(s) at the bridgehead position(s). Studies aimed at the generation and spectral investigation of these cationic species under long-life conditions will most certainly be forthcoming as the peculiarity of the fenestrane framework reveals itself in the appearance of new and unusual structural effects. 

It is also relevant to add that while the experimental studies in this area have actually originated from rather abstract considerations advanced by organic chemists, the fenestrane-like design had been employed in Nature for a long while in the creation of the framework of several natural compounds (such as laurenene 146). What their functions are and how (or if) the functions are related to the specificity of their structure are still questions to be answered. It is also worth noting that synthesis of 146 was achieved rather easily (see refs, in 22b) by employing the methods elaborated in the course of studies aimed at the preparation of the fenestrane framework. 

Centropolyindanes constitute a complete family of arylaliphatic polycyclic hydrocarbons containing several indane units. Mutual fusion of the five-membered rings leads to three-dimensional, carbon-rich molecular frameworks bearing a central carbon atom, such as benzo-annelated [3.3.3]propellanes, triquinacenes, and [5.5.5.6]- and [5.5.5.5]fenestranes. In this review, the structural concept of centropolyindanes is contrasted to other fused indane hydrocarbons. Besides the syntheses of the parent centropolyindanes and recently described related indane hydrocarbons, the preparation of a large variety of bridgehead and arene substituted centropolyindanes is presented including strained, heterocyclic, and centrohexacyclic derivatives. In appropriate cases, the particular reactivity and some structural features of these unusual, sterically rigid polycyclic compounds are pointed out. 

The development of benzoannelated fenestranes has opened several interesting perspectives. Some of them concern structural problems of fenestrane chemistry [34-37,40,117], mostly related to the planar-tetracoordinate carbon problem [118-120]. In this context, the generation of strained cis,cis,cis,trans-... 

Keese R (1987) Planarization of Tetracoordinate Carbon. Synthesis and Structure of [5.5.5.5]Fenestranes. In Chizhov O (ed) Organic Synthesis Modern Trends. Blackwell, Oxford, p 43 Luef W, Keese R (1993) Planarizing Distortions in Carbon Compounds. In Halton B (ed) Advances in Strain in Organic Chemistry, vol 3. JAI Press, Greenwich CT,... 

Krohn K (1991) Fenestranes a Look at Structural Pathologies . In Mulzer J,Altenbach HJ, Braun M, Krohn K, Reissig HU (eds) Organic Synthesis Highlights. VCH Publishers, Weinheim, p 371... 

Planar carbon has long been a subject of experimental and theoretical efforts. Preparation of fenestranes was thought to be one approach but even the latest well-characterized structure, cri,cri,di,rrani-[5.5.5.6]tribenzofenestranehas central bond angles distorted only to 120.8 and 115.5° (Scheme 2.1)." ... 

There has been greater synthetic activity in this series of fenestranes than in any other. The first simple member of the series to be prepared was tetraketone 69 . This synthesis by Cook, Weiss and their coworkers is the prototype of several studies by these investigators. In the case at hand, 70 could be cyclized to 69 in good yield in hot cumene-diglyme containing a large quantity of 1-naphthalenesulfonic acid. An X-ray study confirmed the structure of 69 and showed that in the crystal the molecule exists in a chiral... 

Keese and coworkers have also used the intermolecular arene-alkene photocycloaddition reaction as a key step in another route to [5.5.5.5]fenestranes. Irradiation of 84 gave a mixture of products from which the desired adduct 85 could be isolated. Structure and stereochemistry of this tricyclic ester are supported both by earlier experience with the... 

Sometimes, unactivated alcohols can be converted directly into amines. Denmark et al. were pursuing the synthesis of the structurally interesting fenestranes when they employed an intramolecular Mitsunobu reaction to form compound 106 in 87% yield as the borohydride derivative. ... 

According to the principle of structure stability established by Fernandez and Sinanoglu [8, 9] a maximum or a minimum must exist on a PES between any two saddle points linked by a gradient line. It was, however, stressed that many real PES s, whose form does not follow, for example, the condition of nondegeneracy of the second derivatives matrix, do not necessarily obey this principle [10]. For another example of two consecutive transition state structures see the case of enantiotopomerization of the [4.4.4.4] fenestrane anion [11]... 

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