Diastereo‐ and enantioselective synthesis of 1,2:5,6‐diepoxy‐4‐hydroxyalkyl carbamates. – regioselective ring opening and their transformation into doubly C ‐branched deoxy sugar analogues

Enantiomerically enriched (Z)‐ anti ‐3,5‐dialkyl‐4‐hydroxy‐1,5‐alkadienyl N,N ‐diisopropylcarbamates 12 , readily obtained by the homoaldol approach, were oxidized with essentially complete diastereoselectivity to afford 1,2:5,6‐diepoxides 14 of D‐ allo configuration. Conditions were worked out for the transformation of 14 into furanosides of types 19, 21 , and 22 and for the selective nucleophilic introduction of carbon residues into the 6‐position to give chain‐elongated analogues 25 . Altogether, a “brick‐box system” for the enantioselective construction of polystereogenic building blocks with a few synthetic steps from simple achiral starting materials [( E )‐2‐alkenyl carbamates of type 9 and 2‐alkyl‐2‐alkenals ( 11 )] and nucleophiles, like Grignard reagents, is demonstrated.