ABSTRACT
Chiral interlocked molecules in which the mechanical bond provides the sole stereogenic unit are typically produced with no control over the mechanical stereochemistry. Here we report a stereoselective approach to mechanically planar chiral rotaxanes in up to 98:2 d.r. using a readily available α-amino acid-derived azide. Symmetrization of the covalent stereocenter yields a rotaxane in which the mechanical bond provides the only stereogenic element.
ABSTRACT
To improve access to a key synthetic intermediate we targeted a direct hydrobromination-Negishi route. Unsurprisingly, the anti-Markovnikov addition of HBr to estragole in the presence of AIBN proved successful. However, even in the absence of an added initiator, anti-Markovnikov addition was observed. Re-examination of early reports revealed that selective Markovnikov addition, often simply termed "normal" addition, is not always observed with HBr unless air is excluded, leading to the rediscovery of a reproducible and scalable initiator-free protocol.
ABSTRACT
Lithiation/borylation methodology has been developed for the synthesis of acyclic quaternary-tertiary motifs with full control of relative and absolute stereochemistry, thus leading to all four possible isomers of a stereodiad. A novel intramolecular Zweifel-type olefination enabled acyclic stereocontrol to be transformed into cyclic stereocontrol. These key steps have been applied to the shortest enantioselective synthesis of (-)-filiformin to date (9 steps) with full stereocontrol.
Subject(s)
Bromobenzenes/chemical synthesis , Boronic Acids/chemistry , Bromobenzenes/chemistry , Carbamates/chemistry , Esters , Lithium/chemistry , StereoisomerismABSTRACT
The first total synthesis of (+)-giganin and its unnatural diastereoisomer (+)-C10-epi-giganin has been completed in a total of 13 linear steps, and 7 % and 8 % overall yield, respectively (see scheme; (-)-sp= (-)-sparteine, (+)-sps=(+)-sparteine surrogate). Lithiation-borylation methodology has been successfully applied in the key step, to couple together advanced intermediates with very high diastereoselectivity, thus demonstrating its power as a tool for total synthesis.
Subject(s)
Acetogenins/chemical synthesis , Boron Compounds/chemistry , Lithium Compounds/chemistry , Acetogenins/chemistry , Chemistry Techniques, Synthetic/methods , Molecular Structure , StereoisomerismABSTRACT
(-)-Sparteine induced lithiation of primary 2,4,6-triisopropylbenzoates and subsequent homologation of boronic esters is reported. A comparative study with lithiated N,N-diisopropylcarbamates has demonstrated the superiority of the hindered benzoate.