Diels-Alder adducts barrelenes

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). 

Other heterodienophiles include diethyl azodicarboxylate, tosyl cyanide and phosphaalkynes. Barrelene, benzobarrelene and 2,3-naphthobarrelene react at 100-110 °C (sealed tube) with diethyl azodicarboxylate to give as the main product the corresponding homo-Diels-Alder adduct 27. ... 

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... 

Syntheses have been reported of barrelene (505) and of Nenitzescu s hydrocarbon (503) on a reasonable scale and without some of the difficulties that attend the previously published routes." " The preparation of (503) is of central importance, it being obtained by the oxidative bisdecarboxylation of the cyclo-octatetraene-maleic anhydride Diels-Alder adduct (502) with dicarbonylbis(triphenylphosphine)-nickel in diglyme at reflux. Cycloaddition of (503) to 2,5-dimethyI-3,5-diphenyl-cyclopentadienone in hot benzene afforded (504) and its endo-isomer. Photolysis of (504) yielded (505) in 24% yield from cyclo-octatetraene. The thermally labile benzene-maleic anhydride [4 + 2] cycloadduct (506) was obtained in similar fashion from (502). A review of the mechanisms of pyrolysis of (503) and a number of isomers and benzo-fused (CH) derivatives (collectively termed Nenitzescu s hydrocarbons) has appeared." ... 

Norbornadiene adds typical dienophiles in a homo-Diels-Alder reaction whereby, for example, the adduct 86 is obtained with tetra-cyanoethylene. Dimethyl acetylenedicarboxylate and dicyanoacetyl-ene add to barrelene (bicyclo[2.2.2]octa-2,5,7-triene) in a similar way. °... 

Diels-Alder type of cycloreversions are frequently observed among the azide adducts from barrelenes. The triazoline reaction product from phenyl azide and tetrafluorobenzobarrelene has never been isolated because of the ease with which it undergoes cycloreversion (Scheme 140).166 A similar reaction occurs with 1,4-diphosphabarrelene (see Scheme 23)167,168 as well as with the ethylazidoformate adduct of tetrafluorobenzodihydrobarrelene.169... 

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