Numerous O (oxa)- and S (thia)-glycosyl esters and their analogous glycosyl
acids have been accomplished through stereoselective glycosylation of various peracetylated
bromo sugar with benzyl glycolate using InBr3 as a glycosyl promotor followed
by in situ hydrogenolysis of resulting glycosyl ester. A tandem glycosylating and hydrogenolytic
activity of InBr3 has been successfully investigated in a one-pot procedure. The
resulting synthetically valuable and virtually unexplored class of β-CMGL (glycosyl acids)
could serve as an excellent potential chiral auxiliary in the asymmetric synthesis of a
wide range of enantiomerically pure medicinally prevalent β-lactams and other bioactive
molecules of diverse medicinal interest.
Herein, we report the approach to the otherwise hardly accessible dibenzoxanthenes, diarylbutanes, and calix[4]resorcinarenes possessing urea moieties based on the reaction of N-(4,4-diethoxybutyl)ureas with electron-rich aromatics in strongly acidic media. Unlike the previously developed methods, the proposed approach benefits from one-pot procedure and allows to obtain the target compounds with much higher yields.
An improved protocol for the synthesis of enantiomerically pure allylic amines is reported. N-Protected α-amino esters derived from natural amino acids were submitted to a one-pot tandem reduction–olefination process. The sequential reduction with DIBAL-H at −78 °C and subsequent in situ addition of organophosphorus reagents yielded the corresponding allylic amines without the need to isolate the intermediate aldehyde. This circumvents the problem of instability of the aldehydes. The method tolerates well both Wittig and Horner–Wadsworth–Emmons organophosphorus reagents. A better Z-(dia)stereoselectivity was observed when compared to the previous one-pot method. The (dia)stereoselectivity of the process was affected neither by the reaction solvent nor by the amount of DIBAL-H employed. The method is compatible with the presence of free hydroxy groups as shown with serine and threonine derivatives.
The “one-pot” synthesis of several homochiral macrocycles has been achieved by using π-electron-rich, electron-deficient or extended aromatic dicarboxylic acids in combination with an axially-chiral dibenzylic alcohol, derived from enantiomerically-pure BINOL. Two series of cyclic adducts with average molecular D
2 and D
3 molecular symmetries, respectively, have been isolated in pure forms. Their yields and selectivities deviate substantially from statistical distributions. NMR and CD spectroscopic methods are efficient and functional in order to highlight the variability of shapes of the covalent macrocyclic frameworks. The larger D
3 cyclic adducts exhibit recognition properties towards C60 in toluene solutions (up to log K
a = 3.2) with variable stoichiometries and variable intensities of the charge-tranfer band upon complexation.
One-Pot Synthesis of Novel Dibenzoxanthenes, Diarylbutanes, and Calix[4]resorcinarenes via Consecutive Pyrrolidine Ring-Closure/Ring-Opening Reactions