Highly 1,2-trans Stereoselective Allylations of 1,2-O-Isopropylidene-Protected Glycofuranosides

Enantioselective Synthesis of Medium-Sized Ring-Bridged Oxabicycles by Ring-Closing Metathesis

“…The 2,5‐ cis geometry of the alkenyl chains must bring the diene termini into close proximity and so reduce the entropic cost associated with the ring‐closing process. The exo ‐directed allylation7 of the bicyclic acetals II and ent ‐II should permit access to olefins III and ent ‐III , respectively, as diastereomerically pure compounds. The bicyclic acetal II is obtained from diol I through the Suárez protocol,8,9 which relocates the original anomeric position of D ‐mannose to the new one created by β‐fragmentation at the anomeric position, and traps the intermediate by the secondary hydroxy group placed on the chain (*‐marked oxygen atom).…”

“…Basic hydrolysis and reprotection of the hydroxy group as its tert ‐butyldimethylsilyl ether gave the acetal 10 in a yield of 91%. The exo ‐directed allylation7 of this bicyclic acetal gave the alkene 11 as a unique diastereomer in 85% yield. Protection of the secondary hydroxy group as its tert ‐butyldimethylsilyl ether followed by DIBAL deprotection of the primary pivaloyl ester gave the alcohol 13 in a yield of 86%.…”

Advances in Total Synthesis of Some 2,3,5‐Trisubstituted Tetrahydrofuran Natural Products

“…[89] Opening of epoxide with n-BuLi/CuI addition gave 136 in 76% yield. Next, benzyl protection of free alcohol, followed by Callylation using allylTMS and BF 3 • OEt 2 [90] furnished the mixture of αand β-C-allylglycosides 216 a and 216 b in 3 : 7 ratio. Subjecting these separately to Mitsunobu inversion, terminal olefin oxidative cleavage to aldehyde and two-carbon Wittig homologation delivered unsaturated esters 217 a and 217 b, respectively.…”

The Chiron Approach to (3R,3aS,6aR)-Hexahydrofuro[2,3-b]furan-3-ol, a Key Subunit of HIV-1 Protease Inhibitor Drug, Darunavir

“…Catalytic hydrogenation of olefin 6 over 10% Pd/C in ethanol at 23 °C under a hydrogen-filled balloon afforded saturated derivative 7 as the only isolated product in 96% yield. Saturated ester 7 was converted to γ-lactone derivative 8 by exposure to BF 3 ·OEt 2 (8 equiv) followed by Et 3 SiH (3 equiv) in CH 2 Cl 2 at −78 to 23 °C for 6 h. , Bicyclic lactone 8 was isolated in 87% yield. Presumably, the reaction of the isopropylidene derivative with a Lewis acid resulted in the formation of an oxocarbenium ion intermediate.…”