Highly stereoselective synthesis of perhydropyrano[2,3-b]pyrans from the new 3-methylidenepentane-1,5-dianion synthon

A facile method for the synthesis of fused perhydropyrano[2,3-b]pyrans promoted by Yb(OTf)3

A stereospecific three-component domino reaction between glycals, alkylidene malonate and aldehydes catalyzed by Yb(OTf)3 is described. Multi-substituted cis-fused perhydropyrano[2,3-b]pyran derivatives were obtained with high diastereoselectivity.

Asymmetric Organocatalytic One-Pot, Two-Step Sequential Process to Synthesize Chiral Acetal-Containing Polycyclic Derivatives from Cyclic Hemiacetals and Enones

We have developed an efficient one-pot, two-step sequential process to synthesize biologically and synthetically important chiral acetal-containing polycyclic derivatives. This novel protocol had been proved to proceed via Michael-lactolization-oxocarbenium ion ring-closing sequence, which was initiated by a key reactive enamine intermediate and interrupted the previously established reaction pathway of two different enones used in this work, and generated the corresponding cycloadducts with excellent stereoselectivity bearing up to seven continuous stereocenters. Both chiral and racemic starting cyclic hemiacetals worked well in this strategy. The synthetic applications of the obtained polycyclic products have also been demonstrated.

Functionalised organolithium compounds by sulfur-lithium exchange

Multifunctional organic molecules can be accessed by reacting functionalised organolithium compounds (they can be prepared following a great number of different methodologies) with electrophilic reagents, this fact makes these intermediates of relevant interest in synthetic organic chemistry. Sulfur containing molecules have been used extensively as precursors of organolithium compounds by applying two different methodologies. One is the well-known alpha-deprotonation, which is not going to be the subject of this review, and the other methodology consists of sulfur lithium exchange by using lithium metal either alone or in the presence of a stoichiometric or catalytic amount of an arene. In some special cases, for instance in gem-dithio- or 1,1,1-trithiosubstituted compounds, sulfur lithium exchange can be performed by means of an alkyllithium reagent. The following tutorial review is ordered on the basis of the relative position of the functional group and the carbanionic center, with special mention to the application of these intermediates in organic synthesis.