Base mediated deprotection strategies for trifluoroethyl (TFE) ethers,a new alcohol protecting group

A trifluoroethyl (TFE) ether is specifically introduced as a protecting group in organic chemistry. Its first strategic application and removal in the total synthesis of vinigrol is discussed. Two lithium base mediated deprotection strategies for its removal are presented in this Letter. In one deprotection approach, the trifluoroethyl ether is converted to a difluorovinyl ether and then catalytically cleaved using osmium tetraoxide, while in the second approach a difluorovinyl anion is formed and trapped with an electrophilic oxygen reagent (MoOPH) to form a labile difluoroacetate. To further aid the reader, a summary of approaches for forming trifluoroethyl ethers is included as well as a discussion of alternate deprotection strategies.     

Synthesis of the aglycon of aspafiliosides E and F via a spiroketal-forming cascade

A facile synthesis of C17α-OH-tigogenin, the aglycon of aspafiliosides E and F, is described. The crucial step is the spiroketal-forming cascade, which forms the rings EF in one step and provides a new strategy for spiroketal ring closure in steroidal sapogenins and other substrates. This synthesis minimizes redundant oxidation-reduction manipulations of previous syntheses.     

Design and concise synthesis of gem-difluoromethylenated analogue of 7-epi-castanospermine

A novel gem-difluoromethylenated castanospermine analogue B was designed and synthesized, starting from 3-bromo-3,3-difluoropropene and L-（-）-malic acid. The key steps involve substitution cyclization reaction and RCM reaction to construct the aza fused bicyclic framework.     

A short approach to trisubstituted γ-butyrolactones

The dihydroxylation of unsaturated aldol adducts with catalytic OsO₄ and NMO occurs under very mild conditions and with moderate to excellent levels of diastereoselectivity to give trisubstituted γ-butyrolactone derivatives.     

Synthesis and antimicrobial activity of novel oxysterols from lanosterol

Chemically diverse oxysterols and their synthetic manipulations were carried out from variety of Δ⁸⁽⁹⁾-lanosterol derivatives and evaluated for their in vitro antimicrobial activities. Most of the synthesized oxysterols exhibited significant antifungal activity against the tested strains.     

The stereoselective synthesis of C-linked 4′-deoxy aza-disaccharides from C-linked carbo-β-amino acids

The stereoselective synthesis of 4′-deoxy aza-disaccharides in a concise and practical approach is described from C-linked carbo-β-amino acid esters and this protocol utilizes an intramolecular amide bond formation and cis-dihydroxylation for the construction of the new sugar ring.     

Aminohydroxylation and dihydroxylation of 4-aryl-1,2,5,6-tetrahydropyridines

Substituted 3-amino-4-aryl-4-hydroxypiperidines and 4-aryl-3,4-dihydroxypiperidines are synthesized in the modest overall yields starting from the regio- and stereoselective trans-aminohydroxylation and dihydroxylation of 4-aryl-1,2,5,6-tetrahydropyridines via CAN-mediated oxidative addition and hydrogenation.     

Osmium-catalyzed dihydroxylation of alkenes by H2O2 in room temperature ionic liquid co-catalyzed by VO(acac)2 or MeReO3

Room temperature ionic liquid [bmim]PF₆ was used to immobilize a bimetallic catalytic system for H₂O₂-based dihydroxylation of alkenes. Osmium tetroxide was used as the substrate-selective catalyst with either VO(acac)₂ or MeReO₃ as co-catalyst. The latter serve as an electron transfer mediator (ETM) and activates H₂O₂. For an increased efficiency N-methylmorpholine is required as an additional ETM in most cases. A range of alkenes were dihydroxylated using this robust bimetallic system and it was demonstrated that for some of the alkenes the catalytic system can be recycled and used up to five times.     

Studies directed towards the total synthesis of botcinic acid, the revised structure of botcinolide: synthesis of the highly substituted tetrahydropyran moiety

Synthesis of the highly substituted polyoxygenated tetrahydropyran ring of botcinic acid, the revised structure of botcinolide is achieved using, as key steps, a highly stereoselective aldol reaction of the titanium enolate from a lactate-derived chiral ketone and a stereoselective dihydroxylation.     

Practical dihydroxylation and C–C cleavage of unsaturated fatty acids

Unsaturated fatty acids [C₈H₁₇CH=CH(CH₂)_nCO₂H] (n=7, 11) acids are cleanly dihydroxylated by hydrogen peroxide in the presence of catalytic amounts of H₂WO₄. Under molecular oxygen, in the presence of catalytic amounts of N-hydroxyphthalimide and Co(acac)₃, the diols resulting from erucic (n=11) and oleic (n=7) acid undergo C–C cleavage.