Facile Construction of Spirocyclopropanated Bi‐, Tri‐ and Tetracyclic Skeletons by Novel Cascades Involving Intra‐ and Intermolecular Heck Reactions of 2‐Bromo‐1,6‐enynes and Bicyclopropylidene

Abstract

Keywords: Cyclopropane / Palladium / Transition metal / Cascade reactions / ElectrocyclizationAcyclic 2-bromo-1,6-enynes 5-R, 9-R and 11-R with bulky substituents at the acetylenic terminus were co-cyclized with the highly strained bicyclopropylidene (12) under palladium catalysis at 80°C to give the cross-conjugated tetraenes 13-R, 18-R and 19-R in moderate-to-good yields (34−71%). Only the co-cyclization of 5-Ph gave rise to an additional product, which was identified as the 11-membered ring 20. At elevated temperatures (120−140°C) the initially formed tetraenes underwent 6π-electrocyclization to give spiro [cyclopropane-1,4Ј-bicylo[4.3.0]-1(6),2-dienes] 21-R, 22-R and 23-R. This novel class of spirocyclopropanated oligocycles is also accessible by a one-pot protocol. The highest yields for both

Dendralenes Branch Out: Cross‐Conjugated Oligoenes Allow the Rapid Generation of Molecular Complexity

“…This was followed by an in situ DTDA sequence to give a mixture of four diastereomeric bisadducts 290 (Scheme 51). [74,210] The spiro-cyclopropane ring in product 290 should be readily converted into the gem-dimethyl group. If the two cycloaddition processes can be controlled, this sequence might find application in the total syntheses of terpenoid natural products.…”

“…Cross-coupling methods generally do not lead to the formation of isomeric mixtures and have the added benefit of permitting more highly substituted 1,3-butadien-2-yl coupling partners. [73,74,76] Iododiene 78, for example, was shown by Ma and co-workers to be an effective coupling partner in a Negishi cross-coupling to afford trisubstituted [3]dendralene 80. [75] There are several successful syntheses of substituted [3]dendralenes that proceed through participation of 1,2butadien-4-yl precursors-the allylic transposed form of the 1,3-butadien-2-yl unit (Scheme 15).…”

Transition metals in organic synthesis: Highlights for the year 2005

“…(40)) [468]. Palladium catalyzed an oxidative addition-alkyne insertion-bicyclopropylidene insertion to give cyclopropanated bi-, tri-, and tetracyclic frameworks [469]. Palladium catalyzed the cyclization of aryl halides with tertiary propargylic alcohols to give 3-benzylidene-2,3-dihydrofurans (Eq.…”

Dendralene auf dem Vormarsch: kreuzkonjugierte Oligoene ermöglichen den schnellen Aufbau molekularer Komplexität

“…Kreuzkupplungsmethoden führen im Allgemeinen nicht zur Bildung von Isomerengemischen und haben den zusätzlichen Vorteil, dass sie hçher substituierte 1,3-Butadien-2-yl-Kupplungspartner tolerieren. [73,74,76] Beispielhaft wurde von Ma und Mitarbeitern gezeigt, dass das Ioddien 78 ein effektiver Kupplungspartner in einer Negishi-Kreuzkupplung ist, die zum dreifach substituierten [3]Dendralen 80 führt. [75] Es gibt mehrere Synthesen von substituierten [3]Dendralenen, die auf 1,2-Butadien-4-yl-Vorstufen beruhen -der allylisch transponierten Form der 1,3-Butadien-2-yl-Einheit (Schema 15).…”