Zum Substituenteneinfluß auf die Cope‐Umlagerung von 1,5‐Hexadienen: cyclopropyl‐ und methylsubstituierte Modellsysteme

Abstract

Die neuen 1,S-Hexadienderivate 1 und 2 werden neben allen anderen mdglichen Produkten durch Methylenierung von 1,2,6,7-Octatetraen (5) gewonnen; 2 ist gezielt auch zuganglich aus Succindialdehyd und Cyclopropylidentriphenylphosphoran. Die thermischen Umlagerungen von 1 und 2 verlaufen beide wie die von 5 zweistufig uber 1,4-CycIohexadiyle, aus 1 entsteht neben 3 noch 19, aus 2 nur 4. In dem deutlichen Unterschied der gasphasenkinetischen Parameter fur 2 und 15 (In k(2) = 22.0-26200/RTbzw. In k(15) = 29.1 -33300/RT) kommt zum Ausdruck, daB der Mechanismus der Cope-Umlagerung sich von konzertiert (bei 15) nach zweistufig (bei 2) verschiebt, offenbar aufgrund des Cyclopropyl-Substituenteneffekts. Bei der sensibilisierten Bestrahlung von 2 entstehen die neuen Kohlenwasserstoffe 24, 25 und 27, bei der Nickel(0)-katalysierten Umlagerung ausschlieBlich 25.The new 1,s-hexadiene derivatives 1 and 2 are obtained along with all other conceivable products upon methylenation of 1,2,6,7-0ctatetraene (5); 2 is also accessible from succindialdehyde and cyclopropylidenetriphenylphosphorane. The thermal rearrangements of 1 and 2 both proceed like that of 5 in two steps via 1,4-cyclohexadiyls, 1 yielding 3 and 19, 2 only 4. The distinct differences in the gas phase kinetic parameters for 2 and 15 (In k(2) = 22.0-26200/RT and In k(15) = 29.1 -33300/RT, respectively) indicate the change in mechanism of the Cope rearrangement from concerted (for 15) to stepwise (for 2). apparently due to the cyclopropyl substituent effects. Upon sensitized irradiation of 2 the new hydrocarbons 24,25, and 27 are formed, whereas nickel(0)catalyzed rearrangement of 2 yields 25 exclusively.0 Verlag Chemie GmbH, D-

Intramolecular Heck Couplings and Cycloisomerizations of Bromodienes and Enynes with 1′,1′‐Disubstituted Methylenecyclopropane Terminators: Efficient Syntheses of [3]Dendralenes

“…This corresponds to a remarkably low activation energy for a Cope rearrangement. Even the single other reported example [26] of a Cope rearrangement of a 1,5-diene with a methylenecyclopropane end group most probably has a higher activation energy.…”

Synthesis of Methylene- and Alkylidenecyclopropane Derivatives

“…26 More recently, Cu 2 Cl 2 -catalyzed decomposition of diazomethane served for the cyclopropanation of two bis-allenic compounds 32, which resulted in the formation of all possible mono-and polycyclopropanated derivatives (Scheme 9). 27,28 In the case of biallenyl (n ) 0), formation of both the possible diastereoisomers in about equimolar amounts has been reported for derivatives 37, 40, and 41. 27 In contrast, the same reaction on dicyclopropylidenmethane 42 furnished the monoadduct 43 in 50% yield.…”

“…Photochemical decomposition in the presence of allene gave MCP itself in a 60% yield without the formation of spiropentane or insertion products . More recently, Cu 2 Cl 2 -catalyzed decomposition of diazomethane served for the cyclopropanation of two bis-allenic compounds 32 , which resulted in the formation of all possible mono- and polycyclopropanated derivatives (Scheme ). , In the case of biallenyl ( n = 0), formation of both the possible diastereoisomers in about equimolar amounts has been reported for derivatives 37 , 40 , and 41 …”

“…The olefination through ylide 202 has found many applications in various synthetic strategies. ,,,260a,− Conia's group has synthesized many α-cyclopropylidene aldehydes and ketones by this method . Fukumoto has used alkylidenecyclopropanes 213 obtained by this method for the synthesis of diversely functionalized cyclobutanones on the route to alkylated cyclopentanones (Scheme ) …”

The chemistry of bisallenes

“…The cyclopropanation (CH 2 N 2 , CuCl) of 242 , performed by de Meijere and Kaufmann [176], gave all possible mono- to tetraadducts. As in the case of 2 (see Section 1.4.1, Scheme 46) Scheme 70 only shows a selection of these nine products, 304 – 306 ; to separate and identify these rather similar cyclopropanes constitutes an impressive experimental feat.…”