Fenestrane derivatives

These allylpalladation-acylpalladation cascade bicyclization reactions have been applied mainly by Oppolzer to the synthesis of various natural products including (zb)-pentalenolactone E methyl ester [152], 3-isorauniti-cine [153], ( )-coriolin [154], and ( )-hirsutene [155]. Their application to the syntheses of [5.5.5.5]fenestrane derivatives by Keese [156,157] (Scheme 63) is also noteworthy. 

The photo-Wolff rearrangement has proved of particular value in the synthesis of compounds containing four-membered rings. The first [4.4.4.5]fenestrane derivative (64) to be characterized was obtained in this way by irradiation of the diazocyclopentanone (65) in methanol, and the 4-diazopyrrolidine-2,3-diones (66) have similarly served as useful precursors in a novel approach to /3-lactams (67) and penams. " The related ring contraction... 

In concluding this section on the reactions of propargylium complexes with nucleophiles, we note that use of appropriate unsaturated nucleophiles as reaction partners with the cobalt cations or unsaturated electrophiles in the Ade reaction of Co-compleced 1,3-enynes [213-215] offers an efficient route to variously substituted a,(i)-enynes, valuable precursors for intramolecular Pauson-Khand cyclizations (Scheme 4-64) [96, 98]. This tandem methodology has been employed to produce, among others, bicyclo[3.3.0]octenones and their 3-oxa analogs [22, 216, 217], the fusicoccin sesquiterpenoid skeleton [218], linear and angular fused tri- and tetracyclics [219], and fenestrane derivatives [220]. 

Most importantly, condensed and polycyclic cyclobutane bridgehead derivatives have been synthesized using the photochemical method (Houben-Weyl, Vol. 4/5 b, p 1185). Derivatives of the hitherto smallest and most highly strained [4.4.4.5]fenestrane, methyl 1-methyl-all-ra-[4.4,4.5]fenestrane-7-carboxylate (3a), were formed by irradiation of (la,3/8,6a,9/ )-5-diazo-l-methy][4.4.4.5]fenestran-4-one in methanol.37 Other fenestranes 3b38 and 439 were also formed by irradiation of the corresponding diazocarbonyl precursors. 

A spectacular application allowed the synthesis of fenestranes by a three-step sequential action of cobalt nanoparticles and a palladium catalyst [131]. The cascade reaction started with a PKR of enyne 105, accomplished by the cobalt catalyst giving 106, followed by the formation of allyl-7r3 palladium complex 107 which reacted with a nucleophile derived from diethyl malonate, to give enyne 108. The final step was a second PKR that gave 109 in good yield. They used cobalt nanoparticles as with Co/charcoal the third step did not take place, apparently due to damage in this catalyst after the allylation step (Scheme 31). 

The intramolecular (4n + 4ti) photoaddition of furan-pyran-2-one bichromo-phores [e.g. (38) to give (39)] is potentially useful as an approach towards the fusicoccane/ophiobolane skeleton (Chase et al.), and the formation of (40) from the irradiation of (41) constitutes the first example of a (47t + 4ji) photocycloaddition of an enone to the benzene ring (Kishikawa et al.). Wender et al. continue to report elegant new applications of the intramolecular meta photocycloaddition of 5-phenylpent-l-ene derivatives and have described the synthesis of cis,cis,cis, traMi-[5,5,5,5]-fenestrane (42) using the photoreaction of (43) as a key step. Park... 

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. 

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]... 

You might believe that organic chemists don t have a sense of humor, but there are quite a few jokes in nomenclature (Figure 2.5). With the exception of fenestrane LdXm, fenestra, window), these molecules or their derivatives have all been synthesized. Fenestrane can be made but only when we have at least one 5-membered ring in the structure. Compound 2.15 is called a ladder-ane, and surprisingly, it s a natural product, found in anaerobic ammonia-oxidizing bacteria and synthesized by Corey. 

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