Thermische Umlagerungen von 1‐Allyloxy‐ und 1‐Propargyloxy λ⁵‐phosphorin‐Derivaten

Abstract

Rontgenstrukturanalyse sowie die eindeutigen Deuterierungsergebnisse sprechen fur einen stereochemisch einheitlichen Verlauf der Umlagerungen. Sterische und elektronische Einflusse auf einige analoge Umlagerungen werden untersucht, der Mechanisnus wird diskutiert.Thermal Rearrangements of 1-Allyloxy-and I-Propargyloxy-A5-phosphorin Derivatives The thermal rearrangements of l-allyloxy-h'-phosphorin derivatives 1 affords -contrary to the formally similar Claisen rearrangement of ally1 phenyl ethers -in the irreversible step an ,,antiWoodward-Hoffmann" [3,5,] ally1 shift to 4-allyl-1 ,Cdihydro-h'-phosphorin derivatives 2. -The reaction is, as cross experiments prove, intramolecular and stereospecific according to 1' ' order law. It is accelerated by electron donating substituents in position 4 and by electron attracting substituents at the phosphorus, but is not much solvent-dependant. In a next step, again with allyl-inversion, a [3,3,] Cope rearrangement follows to give 2-allyl-1 ,2-dihydro-h5-phosphorin derivatives 3. At somewhat higher temperature, by an intramolecular [4 + 21-cycloaddition from 3 a tricyclus 4 is formed. Besides the experiments with deuterium marked compounds, the X-ray analysis of 4 proves the uniform stereochemic way of all these rearrangements. Steric and electronic influences on some analogous rearrangements are studied, the mechanism is discussed.I-Allyloxy-1'-phosphorin-Derivate der allgemeinen Konstitution 1 lagern sich beim Erhitzen in indifferenten Losungsmitteln unter Wanderung der Allylgruppe vom Sauerstoff an das Ringkohlenstoffatom 42) in formal ahnlicher Weise wie Allylphenylether bei der Clai~en-Umlagerung~) urn. Der wesentliche Unterschied besteht darin, daB im Primarschritt nicht das 2-sondern das CAllyl-Derivat gebildet wird, wobei zugleich, wie Deuterierungsversuche beweisen, Allylumkehr (la' -+ 2a') eintritt.Die Umlagerung erfolgt somit in einer den Woodward-Hoffmann-Regeln scheinbar widersprechenden [3,5,]-sigmatropen Wanderung. Die Reaktion lafit sich sehr bequem 'H-NMR-spektroskopisch verfolgen und ist irn Gegensatz zu einer friiher beobachteten

Evidence for thermal 3,5-sigmatropy of 7-vinylnorcaradienes

“…3,5-Sigmatropic shifts have occasionally been proposed as steps in complex rearrangement reactions' but in only one case has the process been studied in isolation and evidence for a concerted reaction been obtained. 2 The process may operate in another fairly simple case3 but in other molecules where such rearrangement might have occurred it was not observed. 4 We describe rearrangement of the 7-vinylnorcaradienes (1) to give the 8,9-dihydroindenes (2) and bicyclo[3.2.2]nonatrienes (3) and evidence that formation of the dihydroindenes involves 3,5-sigmatropy (1; arrows) rather than simple vinylcyclopropane rearrangement.…”

[3,3]-Rearrangements of Phosphonium Ylides

“…The earliest characterized example of a phosphonium ylide rearrangement was reported by Baldwin and Armstrong who demonstrated that upon heating, ylide 1 underwent a [2,3]-rearrangement to provide a 7% yield of 2 , along with a number of additional products (Figure ) . Little progress has since been reported, likely due to the apparent propensity of phosphonium ylides to undergo decomposition at the temperatures required for rearrangement. 1c, We hypothesized that structures such as 3 containing an allyloxy substituent would undergo a [3,3]-rearrangement in which the product 4 would be favored thermodynamically due to the formation of the PO bond. In addition, incorporation of the oxygen should increase the leaving group ability of the phosphorus-containing moiety, thus lowering the energetic barrier of the rearrangement …”