Claisen rearrangements potassium acetate

Alkylidene cyclohexenes were synthesized stereoselectively from bis-allyl silylketene acetals derived from cyclohexenones93. As shown in equation 66, Ireland Claisen rearrangement of ester 133 gave only E-diene 136. Reaction of 133 with potassium... 

The decarboxylative Claisen rearrangement of allylic tosylacetate (5) and methyl tosylmalonate derivatives has been extensively studied. In the tosylacetate series, it has been found that acetate ions, base and a silylating agent, preferably N,0-bis(trimethylsilyl)acetamide (BSA), are all necessary, but in only catalytic quantities provided that BSA is used. Potassium acetate has been shown to be a suitable base. 

Still and Schneider employed Ireland-Claisen rearrangement in the total synthesis of ( )-frullanolide (ll)6 (Scheme 1.3f). The key step of the synthesis is efficient Ireland-Claisen rearrangement of the P-pyrrolidinopropionate ester 12. The triethylsilylketene acetal rearranged in toluene at reflux and the pyrrolidine moiety was eliminated after stirring with a mixture of dimethyl sulfate and potassium carbonate in methanol to afford the a-substituted acrylic ester (13). Saponification followed by iodolactonization gave the iodolactone 14, which upon treatment with DBU led to ( )-frullanolide. 

The AG Claisen can be lowered by use of the Ireland variation, as demonstrated by the rearrangement of silyl ketene acetals 221171. In this case, (A , )-l,6-cyclodecadienes can be obtained. However, the result strongly depends on substituent effects. Thus, the Cope-Claisen rearrangement is only successful with substrate 22 c (X = TBDMS), which upon heating to 214 C in 1,2,4-trichlorobenzene in the presence of 10 equivalents of O.A -bis(trimethylsi-lyl)acetamide for two hours followed by treatment with potassium fluoride monohydrate in hexamethylphosphoric triamide and extraction with 1 N potassium hydroxide gives a 9 1... 

CMseH reamuKements. Karanewsky and Kishi have reported that the BOnnal Claisen rearrangement of allyl aryl ethers can be effected in acetic anhydride and sodium or potassium acetate (130-200 ). 

The rearrangement of ketene diallylacetal is of the Claisen type it occurs so readily that the ketene acetal cannot be isolated from the products of reaction of diallylbromoacetal with potassium (-butoxide in f-butyl alcohol.260... 

---