Diels-Alder Cycloaddition: Defucogilvocarcin V (Bodwell), (+)-Carrisone (Danishefsky), (+)-Fusarisetin A (Theodorakis), 9β-Presilphiperfolan-1α-ol (Stoltz), 7-Isocyano-11(20),14-epiamphilectadiene (Shenvi)

Graham J. Bodwell of Memorial University constructed (J. Org. Chem. 2012, 77, 8028) the third aromatic ring of defucogilvocarcin V 4 by the inverse electron demand addition of 1 to 2. The methyl ester 3 provided a useful departure point for the preparation of analogues of 4. Samuel J. Danishefsky of Columbia University and Sloan-Kettering found (Chem. Sci. 2012, 3, 3076) that the kinetic product from the addition of 5 to 6 could be equilibrated with a trace of acid to the more stable regioisomer 7. Oxidation to the enone followed by deoxygenation led to (+)-carissone 8. Michael E. Jung of UCLA developed (Org. Lett. 2012, 14, 5169) Me3Al-triflimide catalysts (not illustrated) for promoting difficult additions such as 5 to 6. Professor Danishefsky had demonstrated the efficacy of cyclobutenones as Diels-Alder dienophiles. More recently, he showed (J. Am. Chem. Soc. 2012, 134, 16080) that intramolecular cyclization of the cyclobutenone 9 led to the transfused, angularly substituted product 11. To prepare (+)-fusarisetin A 14, Emmanuel A. Theodorakis of the University of California San Diego needed (Chem. Sci. 2012, 3, 3378) the all-E geometric isomer of 12. He showed that equilibration of a 3:2 mixture with I2 led to a single dominant isomer that could be taken directly into the cycloaddition. Brian M. Stoltz of CalTech prepared (Angew. Chem. Int. Ed. 2012, 51, 9674) the triene 15 in enantiomerically enriched form by enantioselective allylation of a cycloheptenone derivative. Intramolecular cycloaddition of 15 established the tricyclic skeleton of 9β-presilphiperfolan-1α-ol 17. Ryan A. Shenvi of Scripps/La Jolla devised (J. Am. Chem. Soc. 2012, 134, 19604) the triene 19. Addition of 18 to 19 gave an intermediate that was unraveled with catalytic Yb(OTf)3 to give a trienone, which on heating engaged with the distal alkene to cyclize to 20. This set the stage for diastereoselective conjugate addition leading to 7-isocyano-11(20 ),14-epiamphilectadiene 21.