Synlett 2008(12): 1785-1788  
DOI: 10.1055/s-2008-1078500
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Lewis Acid promoted Oxidative Rearrangement of Tertiary Allylic Alcohols with the PhIO/TEMPO System

Jean-Michel Vatèle*
Institut de Chimie et Biochimie Moléculaires et Supramoléculaires (ICBMS), UMR 5246 CNRS, Université Lyon 1, Laboratoire de Chimie Organique 1, 43 Boulevard du 11 Novembre 1918, Bât CPE, 69622 Villeurbanne Cedex, France
Fax: +33(4)72431214; e-Mail: vatele@univ-lyon1.fr;
Weitere Informationen

Publikationsverlauf

Received 6 March 2008
Publikationsdatum:
19. Juni 2008 (online)

Abstract

A mild and environmentally friendly method for Lewis acid catalyzed oxidative rearrangement of tertiary allylic alcohols to β-disubstituted enones by the TEMPO/PhIO system is described. Bismuth triflate was found to be the most efficient catalyst for the majority of the substrates tested except for tertiary vinyl carbinols which could be transformed to enals in fair yields only when Re2O7 was used as catalyst. A plausible mechanism for this oxidative rearrangement is discussed.

13

General Procedure for Lewis Acid Catalyzed Oxidative Rearrangement of Tertiary Allylic Alcohols with TEMPO and PhIO (Table 2)
To a solution of tertiary alcohol (1 mmol) in CH2Cl2 (5 mL) were added PhIO (264 mg, 2 equiv) and TEMPO (15.6 mg, 0.1 equiv). For method B and C, powdered 4 Å MS was also added (0.08 and 0.13 g/mmol, respectively). The suspension was cooled to 0 ˚C and Lewis acid was added. Dissolution of PhIO is indicative of the end of the reaction. For method A, just after dissolution of PhIO, powdered NaHCO3 was added and the stirring was continued for 10 min. In all cases, the reaction was poured onto a column of SiO2 (20 g) and eluted with EtOAc-PE (1:6). The purity of each synthesized carbonyl compound was checked by NMR spectroscopy.

18

We have shown that allylic alcohols are rapidly oxidized, at 0 ˚C, with TEMPO/PhIO/Yb(OTf)3 system, see ref. 6b.

21

Strong protic acids are known to depolymerize PhIO, see ref. 17b.

23

In order to determine if Re2O7 was able to isomerize allylic alcohols in the lapse of the reaction time (1 h), it was added (8 mol%) to a cooled solution of 1-butyl-2-cyclopenten-1-ol in CH2Cl2. After 15 min, it was observed by TLC the disappearance of the starting material and formation of UV-absorbing, nonpolar products (dehydrated products).