Abstract
Selective oxidations of bis(tricarbonyliron) complexes of methyl (3,7,8‐trimethylidenebicyclo[2.2.2]oct‐5‐en‐2‐ylidene)methyl ketones 15–17 afforded selectively the tricarbonyl {(1__RS__,4__SR__,7__SR__,8__RS__)‐C,7,8,C‐η‐[methyl (3,7,8‐trimethylidenebicyclo[2.2.2]oct‐5‐en‐(2__Z__)‐2‐ylidene)methyl ketone]}iron (12), the corresponding (2__E__)‐derivative 13 and the tricarbonyl{(1__RS__,2__RS__,3__SR__,4__SR__)‐C,2,3,C‐η‐[methyl (3,7,8‐trimethylidenebicyclo[2.2.2]oct‐5‐en‐(2__Z__)‐2‐ylidene)methyl ketone]}iron (18). The stereoselectivity of the Diels‐Alder reactions of the uncomplexed (Z)‐ and (E)‐hexadienone 12 and 13, respectively, was established. The face of the diene syn with respect to the C(5), C(6) etheno bridge was preferred for the cycloadditions of N‐phenyltriazolinedione (NPTAD). In contrast, the reactions of dimethyl acetylenedicarboxylate (DMAD) and methyl propynoate showed a slight preference for addtion to the face of the hexadienones anti with respect to the etheno bridges of 12 and 13. The crystal structure of the adduct 25 resulting from the cycloaddition of NPTAD to 12 is reported.