Octane, Claisen rearrangement

The full paper on the synthesis of onikulactone and mitsugashiwalactone (Vol. 7, p. 24) has been published.Whitesell reports two further useful sequences (cf. Vol. 7, p. 26) from accessible bicyclo[3,3,0]octanes which may lead to iridoids (123 X=H2, Y = H) may be converted into (124) via (123 X = H2, Y = C02Me), the product of ester enolate Claisen rearrangement of the derived allylic alcohol and oxidative decarboxylation/ whereas (123 X = 0, Y = H) readily leads to (125), a known derivative of antirride (126) via an alkylation-dehydration-epoxi-dation-rearrangement sequence. Aucubigenin (121 X = OH, R = H), which is stable at —20°C and readily obtained by enzymic hydrolysis of aucubin (121 X = OH, R = j8-Glu), is converted by mild acid into (127) ° with no dialdehyde detected sodium borohydride reduction of aucubigenin yields the non-naturally occurring isoeucommiol (128 X=H,OH) probably via the aldehyde (128 X = O). ... 

Retro-Claisen rearrangement The formyl bicyclo[2.2.2]octane 1 when heated with a catalytic amount of HO Ac at 110° rearranges to the vinyl ether 2, probably because of relief of the strain associated with the vic-quatemary carbon centers. This retro-Claisen rearrangement occurs rapidly at 0° in the presence of BF3 0(C2H5)2 (0.1 equiv.).10... 

Ramamurthy and coworkers studied the photo-Fries rearrangement of phenyl acetate and phenyl benzoate and photo-Claisen rearrangement of allyl phenyl ether (Fig. 34) included in two types of zeolite (faujasites X and Y and pen-tasils ZSM-5 andZSM-11) [192], The photolysis was performed with the zeolite slurry in either hexane or iso-octane. One of the most remarkable observations is that the product distribution is altered within zeolites from that in isotropic solvent. Furthermore, while in solution, nearly a 1 1 mixture of ortho and para isomers 40 and 41 (Fig. 34) was obtained, within zeolites one is able to direct the photoreaction selectively toward either the ortho or the para products by conducting the reaction either within faujasites or pentasils, respectively (Fig. 34). 

Mandai, Saito and cowoikers recently described a new synthesis of isocaibacyclin, which features a crucial one-pot, three-step transformation tandem tertiary allyl vinyl ether formation, Claisen rearrangement, and ene cyclization led from alcohol (57) directly to bicyclo[3.3.0]octane (59 heme 10). Clearly, due to improvements in the preparation of Ae allyl vinyl ether moiety, there is a trend even in the classical Qaisen rearrangement to taclde more complex structural challenges successfully. 

Formyl bicyclo[2.2.2]octane undergoes retro-Claisen rearrangement to a vinyl ether in the presence of BF3 Et20 at 0 °C (Eq. 49), but not with HOAc at 110 °C [94]. 

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