A New Alkylation Method for Heptalene‐4,5‐dicarboxylates and of One of Their Pseudoester Forms

Dimethyl heptalene‐4,5‐dicarboxylates The locants of heptalene itself are maintained throughout the whole work. See footnote 4 in [1] for reasoning. undergo preferentially a Michael addition reaction at C(3) with α ‐lithiated alkyl phenyl sulfones at temperatures below −50°, leading to corresponding cis ‐configured 3,4‐dihydroheptalene‐4,5‐dicarboxylates ( cf. Table 1, Schemes 3 and 4 ). The corresponding heptalenofuran‐1‐one‐type pseudoesters of dimethyl heptalene‐4,5‐dicarboxylates ( Scheme 5 ) react with [(phenylsulfonyl)methyl]lithium almost exclusively at C(1) of the furanone group ( Scheme 6 ). In contrast to this expected behavior, the uptake of 1‐[phenylsulfonyl)ethyl]lithium occurs at C(5) of the heptalenofuran‐1‐ones as long as they carry a Me group at C(11) ( Schemes 6 and 7 ). The 1,4‐ as well as the 1,6‐addition products eliminate, on treatment with MeONa/MeOH in THF, benzenesulfinate, thus leading to 3‐ and 4‐alkylated dimethyl heptalene‐4,5‐dicarboxylates, respectively ( Schemes 8 – 13 ). The configuration of the addition reaction of the nucleophiles to the inherently chiral heptalenes is discussed in detail ( cf. Schemes 14 – 19 ) on the basis of a number of X‐ray crystal‐structure determinations as well as by studies of the temperature‐dependence of the 1 H‐NMR spectra of the addition products.