The Tandem Michael-aldol Reaction Catalyzed by Trityl Perchlorate

In the presence of a catalytic amount of trityl perchlorate, the tandem reaction of conjugate addition of silyl enol ethers to a,8-unsaturated ketones, and the sequential aldol reaction with aldehydes is carried out smoothly to afford y-acylsubstituted 6-hydroxy ketone derivatives stereoselectively in high yields.The ketones thus obtained are easily converted to tetrahydropyrane or S-valerolactone derivatives.Recently, we have demonstrated new possibilities of various trityl salts in synthetic reactions,' for example, trityl salts efficiently catalyze the aldol reaction between silyl en01 ethers and acetals, orthoesters, or a ~d e h ~d e s .l ~' ~-j Trityl perchlorate also effectively catalyzes the Michael reaction of silyl en01 ethers with a,%-unsaturated ketones, and the adducts, synthetically valuable y- keto silyl en01 ethers, are isolated in high yields.lfAnother advantage of thls reaction is that trityl perchlorate is regenerated owing to the recycle system to coexist with this silyl enol ether after the Michael reaction has completed.Thus, it is assumed that, if appropriate electrophiles are added to the reaction system, it is possible to obtain the adducts by further reactions of the intermediate silyl en01 ethers with various electrophiles.In this paper, we wish to disclose our finding on the trityl perchlorate catalyzed tandem Michael-aldol reaction, and also the utilization of this reaction for the stereoselective syntheses of tetrahydropyrane and 6-valerolactone derivatives.