Variable Strategy toward Carbasugars and Relatives. 4. Viable Access to (4a-Carbapentofuranosyl)amines, (5a-Carbahexopyranosyl)amines, and Amino Acids Thereof

A chiral, divergent synthesis of two carbafuranosylamines, 1 and 2, two carbapyranosylamines, 3 and 4, two carbafuranosylamino acids, 5 and 6, and two carbapyranosylamino acids, 7 and 8, has been achieved. Highlights of the procedure include: a diastereoselective crossed vinylogous Mukaiyama aldol coupling between N-(tert-butoxycarbonyl)-2-ƒË(tert-butyldimethylsilyl)oxyƒÍpyrrole (TBSOP, 9) and 2,3-O-isopropylidene-D-glyceraldehyde (10) for the assembly of the target compound carbon backbone; a high yielding silylative cyclo-aldolization which gives the cyclopentanoid and cyclohexanoid motifs; and a reductive or hydrolytic breakage of the lactam C(O)¡VN link to liberate the carbasugar and install the desired pseudo-anomeric amine and the hydroxymethyl or carboxyl functionalities. The sequences leading to trans-configured carbafuranosyl compounds 1 and 5 and carbapyranosyl compounds 3 and 7 were 12 and 13 step processes, with overall yields of 34%, 35%, 17% and 16%. Cis-configured isomers 2, 4, 6, and 8 were obtained only in minor yields.