Acid allyl esters 1,3-dioxolanes

Sulfuric-fluorosulfonic acid mixtures give complete cyclization of allyl and methallyl esters and thiol esters to give the l,3-dioxolan-2-ylium and l,3-oxathiolan-2-ylium cations (72CRV357) as shown in equation (29). Such cations are frequently involved in the solvolysis of haloacyl derivatives. This neighboring group effect has important mechanistic and stereochemical consequences, and is frequently encountered when working with carbohydrates. 

In the same period, Deng and coworkers also reported that the racemic 5-alkyl l,3-dioxolane-2,4-diones 51 undergo kinetic resolution in the presence of alcohols (ethanol or allyl alcohol) and dimeric cinchona alkaloids such as (DHQD)2AQN (11, 10mol%) [42]. A range of 5-alkyl dioxolanes 51 were highly enantioselectively converted to the (R)-esters (R)-52 (selectivity factors up to 133) (Scheme 11.27). The hydrolysis of the reaction mixture converts the remaining (S)-53 to the (S)-acid (s)-53 that can be easily separated from the (R)-ester 52 by extraction (Scheme 11.27). 

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