Pergamon Tetrahedron Letters 41 (2000) 747–749 TETRAHEDRON LETTERS Phosphazene bases and the anionic oxy-Cope rearrangement Hassan T. Mamdani and Richard C. Hartley * Department of Chemistry, University of Glasgow, Glasgow, G12 8QQ, UK Received 18 October 1999; accepted 10 November 1999 Abstract Compounds containing a 1,5-hexadien-3-ol system undergo anionic oxy-Cope rearrangement when treated with the phosphazene super-base, P 4 -t-Bu. The [3,3] sigmatropic rearrangement occurs in hexane as well as in THF. The weaker phosphazene base, P 2 -Et fails to induce rearrangement. This is the first example of the use of a metal-free base to induce anionic oxy-Cope rearrangement. © 2000 Elsevier Science Ltd. All rights reserved. Keywords: phosphazenes; rearrangements; alcohols; ketones. The anionic oxy-Cope (AOC) rearrangement 1 is the [3,3] sigmatropic rearrangement of an alkoxide 1 generated from a 1,5-dien-3-ol 2 to give an enolate 3 (Scheme 1). The alkoxide 1 rearranges 10 10 to 10 17 times faster than alcohol 2 due to weakening of the C(3)–C(4) bond in the ground state by n- donation from the oxyanion. The n-donation is greatest and the rearrangement fastest when the oxyanion is completely naked; consequently, potassium salts rearrange faster than sodium salts, which rearrange faster than lithium salts. 2 Crown ethers and polar aprotic solvents are often used to reduce association between the oxyanion and the cation. However, metal-free bases have never been used for this reaction. Scheme 1. The phosphazene super-bases 4 and 5, 3 developed by Reinhard Schwesinger, are extremely strong, uncharged, metal-free bases (Fig. 1). We here report that P 4 -t-Bu 4 completely deprotonates alcohol 2 to give alkoxide 1 and a huge ‘soft’ cation, which is known 3 to have its positive charge delocalised over a volume of ca. 500 Å 3 , and that this alkoxide is sufficiently naked to undergo AOC rearrangement. * Corresponding author. 0040-4039/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved. PII: S0040-4039(99)02123-1 tetl 16051