Trimethyl trifluoromethanesulfonate

Even greater diastereoselectivity is achieved by performing the cyclization with silylated malate 12 at —25 °C in the presence of 9 mol% trimethyl trifluoromethanesulfonate. Di-oxolanone 170 is obtained with a cis. trans ratio 100 1 [21]. The stereoselectivity in this reaction is highly temperature dependent. Raising the reaction temperature to 0 °C drastically reduces the cis trans ratio (to 4 1). 

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