Base-Promoted Ring Contractionof Eight-Membered Cyclic Acyloins and their Ethers to C _s-Symmetric α-Ketols

Abstract

In the presence of potassium hexamethyldisilazide and 18-crown-6in THF at room temperature, 2-benzyloxycyclo­octanone andits Δ⁵-unsaturated congener undergo a two-stagere­arrangement to give symmetrical seven-membered ringproducts. The pathway consists of the sequential operation of anO → C 1,2-shift and an α-ketol rearrangement.The greater thermodynamic stability of the cycloheptane or cycloheptenegenerated in this fashion is substantiated by MM3 calculations.

ring contractions - ketones - rearrangements - carbocycles - isomerizations

References

<A NAME="RM01303SS-1">1</A> Paquette LA. Vilotijevic I. Hilmey D. Yang J. Org. Lett.  2003,  5:  463 

<A NAME="RM01303SS-2A">2a</A> Overman LE. Acc. Chem. Res.  1980,  13:  218 ; and references cited therein

<A NAME="RM01303SS-2B">2b</A> Patil VJ. Tetrahedron Lett.  1996,  37:  1481 

<A NAME="RM01303SS-3">3</A> Paquette LA. Zeng Q. Tetrahedron Lett.  1999,  40:  3823 

<A NAME="RM01303SS-4">4</A> Paquette, L. A.; Hofferberth, J.E. Org. React. 2003,in press

<A NAME="RM01303SS-5">5</A>

Several by-products are also generatedunder these longer-term conditions. These proved to be difficultto separate and have not been characterized.

<A NAME="RM01303SS-6">6</A> Kowar TR. LeGoff E. J. Org. Chem.  1976,  41:  3760 

<A NAME="RM01303SS-7">7</A> Allinger NL. Yuh YH. Lii J.-H. J.Am. Chem. Soc.  1989,  111:  8551