Synthese neuer Heptafulvene, Röntgenstrukturanalyse von ‘8,8‐(1′,4′‐Dioxotetramethylen)heptafulven’(2‐(Cyclohepta‐2,4,6‐trien‐1‐yliden)cyclopentan‐1,3‐dion)

Synthesis of New Heptafulvenes; X‐Ray Analysis of ‘8,8‐(1′,4′‐Dioxotetramethylene)heptafulvene’ (2‐(Cyclohepta‐2,4,6‐trien‐1‐ylidene)cyclopentane‐1,3‐dione) Experimental procedures for the synthesis of heptafulvene (3a), 8,8‐tetramethylene heptafulvene (3c) and ‘8,8‐(1′,4′‐dioxotetramethylene) heptafulvene’ (2‐(cyclohepta‐2,4,6‐trien‐1‐ylidene)‐cyclopentane‐1,3‐dion; 3d) are described. The most important sequences include a low‐temperature reaction of tropylium salts with lithium or Grignard carbenoids (Scheme 1) to give 3a and 3b as well as hydride abstraction from substituted cycloheptatrienes followed by deprotonation to give 3c and 3d. Limitations of these sequences are discussed. Two other heptafulvenes 3h and 3i are available by silylation of heptafulvenolates according to well‐known procedures. NMR‐Spectroscopic evidence as well as an X‐ray analysis of 3d are presented. Compound 3d is a relatively polar heptafulvene with a planarised seven‐membered ring as well as a partly delocalized π system.