Rearrangement allyl silyl ethers

Wittig rearrangement of allyl silyl ethers, followed by Simmons-Smith cyclopropana-tion and Collins oxidation, produces a-cyclopropyl acyl silanes, e.g. 22, in 10-85% yields (Scheme 55)85. 

The ozonolysis of substituted-allyl silyl ethers or allyl esters followed by treatment with bases or Ph3P give the corresponding a-silyloxy ketones or a-acyloxy ketones.116 The reaction is proposed to proceed via an ene-diol rearrangement of the corresponding a-silyloxyaldehyde or a-acyloxyaldehydes intermediates. 

The importance of the base used in the [2,3]-Wittig reaction is made clear by the work of Mitchell and coworkers who have reported the rearrangements of silyl- and stannyl-substituted diallyl ethers. They found that the use of LDA on such substrates (38, 41, 43) leads to [2,3]-Wittig reaction while employing lithium diethylamide can result in an allyl-vinyl ether rearrangement instead. 

Danheiser used retro-1,2-Brook rearrangement of allyl silyl ethers in a convenient route to a,/ -unsaturated acyl silanes. For example, 2-methyl-2-propen-l-ol was converted to the trimethylsilyl ether and, in a single-pot process, deprotonated by addition of 1.2 equiv terr-butyllithium. Protonation with a solution of acetic acid in tetrahydrofuran gave the of-hydroxyallylsilane 144. Removal of volatiles from the thermally sensitive product provided 95-percent-pure material that was oxidized to the a,P-unsaturated acyl silane 145 under Swem conditions. ... 

Silyl enol ethers can be prepared from silyl ketones via the Brook rearrangement, and by rearrangement of allylic silyl ethers by a Ru catalyst (Scheme 24). ... 

Siloxycyclopropane 2 rearranged to allyl silyl ether 3 in the presence of catalytic amounts of Zeises dimer (Scheme 2.5) [7]. Deuterium-labeling experiments revealed that the reaction proceeded via formation of platinacyclobutane, het-erolytic cleavage of the Pt-C bond, and a 1,2-hydride shift. 

This effect is the basis of the synthetic importance of ester enolate Claisen rearrangements in which enolates or silyl enol ethers of allylic esters are rearranged into 4-pentenoate esters. 

Silyl ethers of vinyl allyl alcohols can also be used in oxy-Cope rearrangements.215 Known as the siloxy-Cope rearrangement, this methodology has been used in... 

The Claisen rearrangement of allyl vinyl ethers is a classic method for the stereoselective synthesis of y,J-unsaturated esters. The allylic C-H activation is an alternative way of generating the same products [135]. Reactions with silyl-substituted cyclohexenes 197 demonstrate how the diastereoselectivity in the formation of 198 improves (40% to 88% de) for the C-H insertion reactions as the size of the silyl group increases (TMS to TBDPS) (Tab. 14.14). Indeed, in cases where there is good size differentiation between the two substituents at a methylene site, high diastereo- and enantioselectivity is possible in the C-H activation. 

Formation of a silyl enol ether will generate an allyl vinyl ether which after rearrangement can be desilylated to give a carboxylic acid. 

Treatment of silyl ethers of allyl alcohol, and some simple derivatives, with t-BuLi in THF-HMPA, followed by a suitable electrophile, has been shown to give the 1,4-retro-Brook rearrangement products, which are ethers, carbonates or carbamates of... 

This gentle variant of the Claisen Rearrangement employs the allyl ester of a carboxylic acid instead of an allyl vinyl ether. The ester is converted to its silyl-stabilized enolate (silyl ketene acetal), which rearranges at temperatures below 100 °C. 

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