Allenyl Silyl enol ethers

Acylsilanes of a variety of substitution patterns have been employed (9) in routes to allenyl silyl enol ethers. 

Allenyl Silyl enol ethers, 86 Allyl alcohol trimethylsilyl ether, 84 Allyl carbonates, 114-15 9 Allyl-ay 2 octalone, 34-5 2-Allyl-2 methylcyclohexanone, 106 (Allyldimethylsilyl)methyl chloride, 58, 59 (AUyldimethylsilyl)methylmagnesium chloride, 59... 

The most versatile synthesis of w./i-unsaUi rated acyl silanes involves the use of allene methodology, developed by a number of groups14,22. Deprotonation and silylation of allenyl ethers followed by hydrolysis gives rise directly to ,/3-unsaturated acyl silanes via their enol ethers, 1-alkoxy-l-trimethylsilylallenes (Scheme 43). Indeed, the first example of an a,/l-unsaturated acyl silane was prepared by such a route223, as was the first example of an allenic acyl silane (from a l-trimethylsilyl-l-trimethylsilyloxy-l,2,3-alkatriene)22b. 

The reaction of lithium diisopropylamide with propargyl acetate 3.559 followed by treatment of the enolate formed with trimethylchlorosilane at —78°C affords ketene acetal 3.561. After heating the reaction mixture to 40°C, the intermediate vinylpropargyl ether 3.560 undergoes the Claisen rearrangement to produce silyl ester 3.561, which after hydrolysis forms allenyl-acetic acid 3.562 with a 50% overall yield (Scheme 3.42) [281]. This reaction is of interest as a synthetic strategy for obtaining the benzoannelated enyne-allene that by radical cyclization forms polycyclic aromatic compounds with an embedded fluorene section [281]. (Scheme 3.43)... 

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