Showing papers by "Samir Z. Zard published in 2016"
TL;DR: The degenerative reversible transfer of xanthates allows radical addition even to unactivated alkenes and tolerates numerous functional groups, in particular common polar groups such as ketones, esters, amides, carbamates, nitriles etc.
Abstract: The present account summarises routes to organofluorine derivatives based on the chemistry of xanthates developed in the author's laboratory. It concerns mostly radical pathways, but a few ionic transformations are also discussed. The degenerative reversible transfer of xanthates allows radical addition even to unactivated alkenes and tolerates numerous functional groups, in particular common polar groups such as ketones, esters, amides, carbamates, nitriles etc. Since the fluorine atoms can be placed on the alkene or the xanthate partner or on both, this opens a convergent approach to a vast array of otherwise inaccessible organofluorine structures that could be of interest to the pharmaceutical and agrochemical industries and to materials science.
28 citations
TL;DR: A powerful strategy for the regioselective bidirectional synthesis of unsymmetrically substituted ketones is described, relying on the fact that the exchange of a xanthate is much faster than the radical addition to an unactivated alkene.
Abstract: A powerful strategy for the regioselective bidirectional synthesis of unsymmetrically substituted ketones is described, relying on the fact that the exchange of a xanthate is much faster than the radical addition to an unactivated alkene. The use of an alkene as the formal “alkylating” agent associated with the tolerance for numerous functional groups and the mildness of the experimental conditions removes many of the problems associated with the classical ionic and transition-metal-based approaches.
27 citations
TL;DR: A radical based synthesis of a broad variety of protected enantiopure α-amino acids, including fluorinated derivatives, is described, which furnishes naturally latent mercapto-α-aminos acids ideally equipped for native chemical ligation.
26 citations
TL;DR: An overview of a convergent, modular route to protected amines, anilines, and related compounds hinging on the degenerate radical addition-transfer of xanthates is presented in this paper.
Abstract: An overview of a convergent, modular route to protected amines, anilines, and related compounds hinging on the degenerate radical addition-transfer of xanthates is presented. Emphasis is placed on the importance of the stabilization of the starting radical by imides and other structures. 1 Introduction 2 The Degenerate Xanthate Transfer Process and Examples of Amine Synthesis 3 Stabilization of Radicals by Imides. Initial Observations and the Radical Aminomethylation of Alkenes 4 More Elaborate Phthalimide-Substituted Xanthates 5 Polyamines and β-Lactams 6 Anilines and Related Derivatives 7 Further Synthetic Variations 8 Outlook and Perspectives
24 citations
TL;DR: An overview of a convergent, modular route to protected amines, anilines, and related compounds hinging on the degenerate radical addition-transfer of xanthates is presented in this article.
Abstract: An overview of a convergent, modular route to protected amines, anilines, and related compounds hinging on the degenerate radical addition-transfer of xanthates is presented. Emphasis is placed on the importance of the stabilization of the starting radical by imides and other structures. 1 Introduction 2 The Degenerate Xanthate Transfer Process and Examples of Amine Synthesis 3 Stabilization of Radicals by Imides. Initial Observations and the Radical Aminomethylation of Alkenes 4 More Elaborate Phthalimide-Substituted Xanthates 5 Polyamines and β-Lactams 6 Anilines and Related Derivatives 7 Further Synthetic Variations 8 Outlook and Perspectives
3 citations
TL;DR: In this paper, a modification of the von Auwers rearrangement was proposed for 3-methylene-1,4-cyclohexadienes possessing an alkoxy carbonyl substituent in position 6.
3 citations
TL;DR: The S -propargyl xanthate derived from ethyl (S )-lactate reacts upon heating with various acidic substances to give the propionate transfer product in high yield and with complete inversion of configuration.
Abstract: The S -propargyl xanthate derived from ethyl ( S )-lactate reacts upon heating with various acidic substances to give the propionate transfer product in high yield and with complete inversion of configuration.
2 citations
TL;DR: In this article, the radical addition of xanthates to N,N-diacetyl imidazol-2-one can be followed by a second addition to give after reductive dexanthylation a protected tetra-amine possessing four contiguous carbon-nitrogen bonds, if the starting xanthate itself bears a protected amine.
1 citations
TL;DR: In this paper, a simple radical-based route to gem-α-dichloroketones, relying on the degenerative addition transfer of (S)-[3,3-Dichloro-2-oxopropyl]-O-ethyl dithiocarbonate (xanthate), is described.
Abstract: A simple radical-based route to gem-α-dichloroketones, relying on the degenerative addition transfer of (S)-[3,3-dichloro-2-oxopropyl]-O-ethyl dithiocarbonate (xanthate), is described. The adducts can then be converted into Z-enoates by exposure to Et3N in methanol. In the case of certain substrates, it was possible to form skipped dienoic acid and methyl E,E-dienoates.
TL;DR: In this article, a radical based synthesis of a broad variety of protected enantiopure α-amino acids, including fluorinated derivatives, is described, and the radical addition furnishes naturally latent mercapto-α amino acids ideally equipped for native chemical ligation.
Abstract: A radical based synthesis of a broad variety of protected enantiopure α-amino acids, including fluorinated derivatives, is described. The radical addition furnishes naturally latent mercapto-α-amino acids ideally equipped for native chemical ligation.
TL;DR: The degenerative reversible transfer of xanthates allows radical addition even to unactivated alkenes and tolerates numerous functional groups such as ketones, esters, amides, carbamates, nitriles etc.
Abstract: The present account summarises routes to organofluorine derivatives based on the chemistry of xanthates developed in the author's laboratory. It concerns mostly radical pathways, but a few ionic transformations are also discussed. The degenerative reversible transfer of xanthates allows radical addition even to unactivated alkenes and tolerates numerous functional groups, in particular common polar groups such as ketones, esters, amides, carbamates, nitriles etc. Since the fluorine atoms can be placed on the alkene or the xanthate partner or on both, this opens a convergent approach to a vast array of otherwise inaccessible organofluorine structures that could be of interest to the pharmaceutical and agrochemical industries and to materials science.
TL;DR: In this article, a modification of the von Auwers rearrangement was proposed for 3-methylene-1,4-cyclohexadienes possessing an alkoxy carbonyl substituent in position 6.
Abstract: Upon heating, 3-methylene-1,4-cyclohexadienes possessing an alkoxycarbonyl substituent in position 6 undergo rearrangement and concomitant aromatization to give the corresponding arylacetates. This transformation represents a modification of the von Auwers rearrangement and proceeds by a radical chain mechanism. The intermediate alkoxycarbonyl radical can be intercepted allowing further useful synthetic variations.