Showing papers by "Samir Z. Zard published in 2019"
29 citations
TL;DR: Pinacolato boronates (Bpin) as mentioned in this paper stabilize an adjacent carbon radical by alternately placing a pinacol or diethanolamine moiety on the atom, thus stabilizing or not stabilizing the corresponding adjacent radical.
Abstract: Pinacolato boronates (Bpin) with an empty p-orbital on boron stabilize an adjacent carbon radical, in contrast to diethanolamino boronates [B(DEA)] where the boron is sp3 -hybridized. By alternately placing a pinacol or diethanolamine moiety on the boron atom, thus stabilizing or not stabilizing the corresponding adjacent radical, it is possible to control the behavior of α-boronyl xanthates and construct a large variety of terminal or internal boronates in a modular fashion. The remarkable tolerance of polar groups and the ability to introduce quaternary centers are particularly noteworthy features of this process.
26 citations
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6 citations
TL;DR: In this article, the authors discuss the numerous routes to all-carbon quaternary centers based on the unique radical chemistry of xanthates and discuss the intra-and intermolecular radical additions and combinations thereof.
Abstract: This review discusses the numerous routes to all-carbon quaternary centers based on the unique radical chemistry of xanthates. It summarizes the various approaches to the synthesis of tertiary xanthates then describes the intra- and intermolecular radical additions and combinations thereof that have so far been used to construct quaternary centers.
6 citations
TL;DR: S-Propargyl xanthates undergo upon heating a [3,3] sigmropic rearrangement followed by a reversible ring closure into a novel betaine.
Abstract: S-Propargyl xanthates undergo upon heating a [3,3] sigmatropic rearrangement followed by a reversible ring closure into a novel betaine. This betaine can be implicated in carbon–carbon bond forming processes, in the synthesis of esters, in the inversion of secondary alcohols, in the formation of alkenes, for the generation of rigid, cisoid dienes that are highly reactive in both inter- and intra-molecular Diels–Alder cycloadditions, and in various other synthetically useful transformations. 1 Introduction 2 An Unexpected Transformation 3 Evidence for the Betaine Intermediate 4 A Method for the Synthesis of Esters and for the Inversion of Secondary Alcohols 5 A General Alkylation Process 6 The Case of Carbon Acids 7 A Synthesis of Alkenes 8 Further Trapping Experiments. Concerted or Not Concerted? 9 Rigid Cisoid Dienes 10 Propargyl Radicals 11 Concluding Remarks
5 citations
TL;DR: O-Neopentyl-xanthate 19 bearing a masked α-amino aldehyde, with the two functional groups orthogonally protected, reacts cleanly with many functional alkenes and furnishes densely functionalized adducts that can be further transformed into an array of amino-substituted carbocycles and heteroaromatics.
3 citations
TL;DR: A series of conjugated 4-alkenyl-1,3-dithiol-2-ones have been prepared by microwave-assisted rearrangement of S-(4-acyloxy- 2-alkynyl)- O-ethyl xanthates in moderate to good yields by a combination of [3,3] and [1,5] sigmatropic rearrangements.
2 citations