Furans retrograde Diels-Alder reactions

Di-f-menthyl acetoxymethylenemalonate (67) is another chiral dienophile that has been utilized in asymmetric Diels-Alder reactions [51]. High-pressure-mediated addition of 67 to furan produced a mixture of labile endo and exo cycloadducts (i.e., 68) that were immediately converted into the corresponding acetonides 69. The reductive retrograde aldol reaction of the entio-product 69 resulted in the formation of (3-D-ribofuranosylmalonate 70. Analogous manipulation of the exo product gave the corresponding synthetic L-analog (Scheme 13.21) [51]. 

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