Synthesis of Protected Carbohydrate Derivatives through Homologation of Threose and Erythrose Derivatives with Chiral γ-Alkoxy Allylic Stannanes

Article abstract of DOI:10.1021/jo00091a034

Additions of the γ-alkoxy allylic stannanes (S)-1 and (R)-1 and the racemate (RS)-1 to the threose and erythrose aldehyde derivatives 6 and 15 in the presence of BF3*OEt2 or MgBr2*OEt2 were examined in order to establish stereochemical preferences.It was found that (S)-1 and aldehyde 6 afforded the syn,anti,syn adduct 7 in the BF3-promoted reaction, while (R)-1 and 6 gave the syn,syn,syn adduct 8 under MgBr2 conditions.Likewise, (S)-1 and aldehyde 15 yielded the syn,anti,anti adduct 16 with BF3, whereas (R)-1 and 15 led to the syn,syn,anti adduct 17 with MgBr2.The MgBr2-promoted reactions showed sufficient rate differences between the matched and mismatched stannanes to allow the use of racemic stannane (RS)-1 in just over 2-fold excess, whereupon the matched adducts 8 and 17 were favored by greater than 9:1 over the mismatched adducts.The major adducts 7, 8, 16, and 17 were converted to the hexose derivatives 21, 30/31, 34, and 39 by ozonolysis, selective deprotection, and refunctionalization.Adducts 16 and 17 were dihydroxylated with OsO4-NMO to the deoxyoctose precursors 40/41 and 42/43.