Barrelenes synthesis

Oxepin is in equilibrium with benzene oxide by a [3,3]-sigmatropic shift. Advantage has been taken of this equilibrium to develop a short synthesis of barrelene. Outline a way that this could be done. 

Synthetic applications of other decarbonylation reactions are found in the conversion of cyclooctatetraene to barrelene 250), with the photodecarbonyla-tion of a Diels-Alder adduct as key step (2.31) and the preparation of tetrathioesters from 1,3-dithioles (2.32) 251). The most remarcable application of such a reaction up to date is the synthesis of tetra t.butyltetrahedrane from a tricyclic ketone precursor (2.33) 252). 

The synthesis of tri-/-butyl-lP,32, 5A -triphosphinine arose from studies of the behavior of t-butylphosphaethyne (206) in the coordination sphere of transition metals. The first indication of the transition metal template catalyzed trimerization of (206) was the isolation of the vanadium-complexed 1,3,5-triphospha-Dewar benzene (207) <87AG(E)908>. The formation of the tetra-phosphabarrelene complexed to zirconium (208) implied the intermediate formation of the com-plexed tri-(-butyltriphosphinine derivative. The free barrelene could be obtained by oxidative decomplexation using C2CI6 <95AG(E)8i>. 

The reactions of the strained benzene derivative 25 with DCA were originally studied with the aim of synthesizing planar cyclooctatetraene derivatives which are interesting compounds with respect to the question of their antiaromaticity [56]. The cyclooctatetraene derivative, 29 (Scheme 2.9) synthesized by photolysis of the barrelene derivative 26, however, turned out to be non-planar [57]. But the synthesis and the reactions of barrelene derivative 26 are interesting with respect to the utility of high pressure to control the course of reaction. The reaction of 25 with DCA at 1 bar and 127 °C produces the (1 1) Diels-Alder adduct 26 (yield, 49 %) and the unexpected dark blue (2 1) adduct 27 (yield, 14 %). At high pressure (9 kbar, 83 °C) 27 is the major product even after the low conversion of 36 % of the... 

The same concept has been extended to the synthesis of aromatic and heteroaromatic compounds bearing two 1-adamantyl substituents <90JA5654> and two neopentyl substituents <94TL2709> at ort/io-positions. Interestingly, the reaction of 3,4-dineopentylthiophene-1,1-dioxide with benzyne (from 2-carboxybenzenediazonium chloride) gives (217) as the major product (68%) via an ene reaction the cycloadduct-S02 extrusion product (218) is formed in 20% yield. The latter undergoes further cycloaddition with another molecule of benzyne to give a dibenzo barrelene derivative (7.5%). The formation of such barrelene derivatives had been observed earlier with a few other thiophene-1,1-dioxides as well <86H(24)1233>. 

Oxidative bisdecarboxylation. An efficient recent synthesis of Nenitzescu s hydrocarbon (3) involves a Diels-Alder reaction followed by bisdecarboxylation with this Ni complex. Pb(OAc)4 is unsatisfactory for the latter step. The product (3) was also used for preparation of barrelene (4) in 24% yield from (1). 

Other Octacarbonyidicobalt-Catalyzed Reactions. A retro-Diels-Alder reaction catalyzed by Co2(CO)8 was observed in which a barrelene derivative loses a C2H2 fragment (eq 30). An analogous cleavage accompanies the cyclopentenone synthesis (see below) when norbomadiene reacts in certain solvents with alkynehexacarbonyldicobalts, as shown by the formation of dicarbonylcyclopentadienylcobalt, whereas a Diels-Alder addition catalyzed by a cobalt carbonyl species is involved when the same reaction is applied to cyclohexadiene. ... 

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