Bicyclo octenones rearrangement

Another example of suprafacial migration with inversion is the rearrangement of bicyclo octenone to give again a ketone and reported by J.A. Berson (1972). 

Highly strained substrates can be transformed into even more strained isomers by ODPM rearrangement. This has been shown by Murata et al. for the synthesis of a valence isomer of azulene [45]. Albeit the photochemical reaction yielded only 20-25% of the bicyclo[1.1.0]butane derivative 15, the synthesis of the precursor cyclobutene (14) is straight-forward from the bicyclo[3.3.0]octenone 13 (Sch. 18). This substrate has obviously a diverse reactivity pattern when directly excited, however, triplet sensitization reduces these competitive pathways because alkene excitation is excluded. Also benzo-annulated azulene valence isomers were generated by this approach [46]. 

The photolyses of conformationally fixed 3,y-unsaturated ketones can also be performed in constrained media. This was described for the ODPM rearrangement of bicyclo[2.2.1]heptenone and bicyclo[2.2.2]octenone in MY zeolites [47]. It is remarkable that direct irradiation of the guest-incorporated thallium-Y (TIY) zeolites at 254 nm resulted in higher yields of ODPM products than the triplet-sensitized solution photolyses (Sch. 19). This indicates that the triplet carbonyl species are generated more efficiently in the supercages of the zeolites presumably because of the presence of heavy... 

If rapid bond formation at the stage of the Norrish I fragments competes with decarbonylation, 1,2-acyl shift products are formed as the major components from direct photolysis. In case of the cyclobuteno-annulated bicyclo[2.2.2]octenone 21, 1,2-acyl shift results in the cyclo-butanone 22, whereas ODPM rearrangement (photolysis in acetone) results in the cyclobuteno-diquinane 23 in 44% yield (Sch. 21) [49]. 

In sole conflict with this coherent picture of the correlation of excited states and reactivity in the ODPM context is the claim that a representative of the 1-methoxy-substituted bicyclo[2.2.2]octenones [cf. (66a) in Scheme 13, Section 2.6.3.4.2] may not necessarily rearrange from the Ti state but rather from TzP" ... 

The rearrangement of 1-methoxy-substituted bicyclo[2.2.2]octenones (66a-d) follows a mechanistic variant of the ODPM reaction, which includes two consecutive single-step phototransformations, i.e. the ODPM path to (67a-d), again triplet sensitized, and conversion to the final 1,4-diketones (68a-d) cf. Scheme 13).5-1U05-108 jjjg second step involves cleavage of the transient cyclopropane in (67a-d) accompanied by loss of the methoxy methyl, most likely via methyl radicals, and transfer of a hydrogen atom from the solvent. 

The conversion of a bicyclo[2.2.1]octenone derivative to the corresponding bicyclo[3.3.0]octenone, a common intermediate in the total synthesis of several iridoid monoterpenes, was achieved by N.C. Chang et al. The target was obtained by sequential application of the Corey-Chaykovsky epoxidation, Demjanov rearrangement and a photochemical [1,3]-acyl shift. 

In contrast, treatment of the bicyclo[2.2.2]octenone bearing a nitro (NO2) group with KHMDS led only to the epimerization of the C-7 stereocenter in the substrate, whereas KH in THF or NaH in DMF induced the acyloin rearrangement in good yields. 

Scheme 9.15 S5mthesis and ODPM rearrangement reaction of a cyclopentannulated bicyclo[2.2.2]octenone leading to a cyclopropannulated linear triquinane.

Finally, a methylene-linked and readily accessible cyclopentannulated bis-bicyclo[2.2.2]octenone has been shown to undergo a two-fold ODPM rearrangement reaction and thereby affording bis-linear triquinanes possessing a bird-shaped architecture. ... 

Photochemical oxa-di-jt-methane rearrangement of bicyclo[3.2.1]octa-noid scaffolds affords multifunctional, donor-acceptor cyclopropanes (34). Application of this reaction to bicyclo[2.2.2]octenones has been used as a key step in the total synthesis the hirsutane-type sesquiterpenes (-)-connatusin A (35), (+)-connatusin B (36), and the marine sesquiterpenoid 2-isocyanoallopupukeanane (37). ... 

In 2013, Liao reported the first asymmetric total syntheses of the sesquiterpenoid lactones (+)-eudesmadiene-12,6-olide and (+)-fruUanolide, which were based oti an initial dearomatization of 4-bromo-2-methoxyphenol 240 into the corresprMidmg MOB 241 (Fig. 58) [129]. An asymmetric Diels-Alder reaction wifli the chiral furan R)-2A2 furnished the bicyclo[2.2.2]octenone 243 in good yield with high chemo-, regio-, and stereoselectivities. This compound was further transformed in a few steps to reach (+)-eudesmadiene-12,6-olide, whose m-decalin core was elaborated by a high-yielding anionic oxy-Cope rearrangement of the allylic alcohol 244 (Fig. 58) [129]. 

Bicyclo[2.2.1]heptenones Bicyclo[3.2.1]octenones and Congeners Bicyclo[2.2.2]octenones Oxa-di-JC-methane Rearrangements in Polycyclic-Bridged P.y-Enones ... 

Singh, V.K., Deota, RT., and Bedekar, A.V., Studies in the synthesis of polycyclopentanoids synthesis, oxa-di-7i-methane rearrangement of annulated bicyclo[2.2.2]octenones and cyclopropane ring cleavage of tetracyclo[6.3.0.0. > 0 > ]undecenones,/. Chem. Soc., Perkin Trans. 1, 903,1992. 

Singh, V. and Jagadish, B., Synthesis of exo-annulated bicyclo[2.2.2]octenone and its oxa-di-Jt-methane rearrangement to cisisynxis triquinane, Indian J. Chem., 35B, 401,1996. 

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