Palladium-catalyzed cyclizations of the 2-bromo-1,6-diene 6 57 with a methoxycarbonyloxymethylene substituent on the triple bond gave in 36% yield the 2,3-bis(bicyclo[3.1.0]hex-with an acetoxymethyl substituent on the bromoalkenyl moiety did not only lead to the expected 1-acetoxymethyl-1-yl)-substituted 1,3-butadiene 63, which can be regarded as a dehydrodimer of the vinylcyclopropane 35. The 1,3-diene 40 but also to the bicyclic vinylcyclopropane 35, the 1,3-diene 36 and the triene 37 (a dendralene). All these presumption that the formation of 63 involves the alkenylpalladium species 65 was supported by its successful compounds result from an initial 5-exo-trig cyclization of the 2-bromo-1,6-diene. By proper choice of the reaction inter-as well as intramolecular trapping with formate as a hydride source to yield the vinylcyclopropane 35. The conditions (ligand, base, allylic leaving group) each of these compounds could be formed selectively. Small amounts (3-reaction pathways leading to the vinylcyclopropane derivatives 35 and 63 have in common that an 5%) of the isomerized 1-acetoxymethyl-1,3-diene 38 and the 6-endo product 39 were also isolated. With the alkylpalladium species rather undergoes a 3-exo-trig cyclization than an internal rotation followed by a β-acetoxymethyl substituent on the alkenyl moiety (compound 27) only the 1,4-diene 44 was formed. The related 1,6-enyne hydride elimination.
with a cyclopropane ring directly attached in a methylene- [a] Institut für Organische Chemie der Georg-August-Universität lyzed Michael addition to methyl acrylate (28) (Scheme 5).
Göttingen,
Most probably, the (Z) configuration of the exocyclic Tammannstraße 2, D-37077 Göttingen, Germany double bond in 31 prevents the system from undergoing the