1.2- cyclopropyl carbohydrates

The ring-opening reaction of functionalized 1,2-cyclopropyl carbohydrates is also known, apart from that of unfiinctionalized derivatives. Yu and Pagenkopf demonstrated the formation of oxepine 51 through Ferrier rearrangement-based ring opening... 

Tochtermann reported the addition of dichlorocarbene to the racemic glycal 52, whose cyclopropyl-allyl rearrangement leads to the 2//-pyran. The synthesis of the optically pure (+)-(2S,3R,7S) and (-)-(2f ,3S,7f )-glycal precursors has also been achieved. As pointed out, optically pure glycals are versatile precursors for carbohydrate synthesis <00EJO1741>. 

The synthesis of gm-diallyl derivatives can be achieved by double alkylation of active methylene groups. We realized that installation of gem-diallyl functionality on a carbon atom, not activated by any electron-withdrawing group, is a difficult proposition. The problem becomes insurmountable on carbohydrate precursors because base-catalyzed reactions lead to tandem elimination of water molecules, resulting in the formation of complex mixtures, We observed interesting reactions with carbohydrate cyclopropyl precursors. For example, the radical-mediated cyclopropyl scission of the spirocyclopropyl bromide (86) with n-BusSnH gave the C-aUyl derivative (87) in a stereo-controlled fashion. On the other hand, hydrogenation of the cyclopropylaldehyde derivative (88) over Pd/C provided 89 with a quaternary chiral center (Scheme 30.14). 

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