Studies on structurally simple butenolides. VI. The polycyclic 3:1 adducts of protoanemonin with C-nucleophiles

X-Ray diffraction analysis yielded the constitution, configuration and conformation of a tetracyclic 3:1 adduct formed by reaction of protoanemonin $\text{1}$ with lithium dimethylcuprate. The same configuration was assigned by analogy to other tetracyclic 3:1 adducts formed by reaction of $\text{1}$ with lithium di-$\text{n}$-butylcuprate or di-methyl sodiomalonate. A pentacyclic 3:1 adduct also formed in the last reaction was fully assigned (constitution, configuration, conformation) by analysis of its 300 MHz 2-D COSY NMR spectrum.