Radical vicinal carbohalofunctionalization of C-C multiple bonds via atom transfer processes constitutes an efficient method for the construction of halgenated building blocks with complete atom economy. This review summerizes the...
Transition-metal-catalyzed 1,2-carbohalofunctionalization reactions of CÀ C multiple bonds have emerged rapidly over the past decade as a powerful tool for generating a new carbon-carbon and carbon-halogen bond via transposition of an existing carbon-halogen σ bond. Exploring this highly efficient mode of carbon-carbon multiple bond difunctionalization, various research groups have established novel strategies for the synthesis of organohalides by utilizing wide variety of transition metal catalysts under mild reaction conditions, avoiding stoichiometric waste of by-products, and with improved levels of chemo-, regio-, and stereoselectivities. Most of the 1,2-carbohalo-functionalization reactions involve either the carbon-halogen reductive elimination mechanism or the atom transfer radical addition (ATRA) mechanism. This review summarizes the recent progress in the area of transitionmetal-catalyzed intra-and intermolecular 1,2-carbo-halo-functionalization reactions of carbon-carbon multiple bonds and explicates the underlying potentiality and challenges within the field.
Herein,
we disclose the first report on iodo-cycloisomerization
of 1-(indol-3-yl)-1-arylbut-3-yn-2-ols to form 3-iodocarbazoles. The
synthesis proceeds through a cascade 5-endo-spirocyclization, followed
by selective 1,2-alkyl migration. This method governs the green synthesis
principles such as open-flask reaction, AcOEt as the solvent, rt reaction
with short time, use of iodine, and broad substrate scope with atom
and step economy.
An unprecedented Au(I)-catalyzed
domino intramolecular carbonyl-alkyne
cyclization/indole addition strategy has been disclosed here. This
generalized strategy enables the synthesis of 3(2H)-furanone-incorporated unsymmetrical bis(indolyl)methanes with generation
of a stereocenter at the furanone junction from easily accessible
indole-tethered ynediones. In addition, this present protocol could
also be extended for the synthesis of a number of indolyl-(hetero)arylmethanes
by employing a variety of (hetero)arenes as a nucleophile coupling
partner.
Heteroarene-tethered functionalized alkynes are multipotents ynthons in organic chemistry.T his detailed Review described herein offers at horough discussion of the metamorphosis of heteroarene-tethered functionalized alkynes, an area which has earned much attention over the past decade in the straightforward synthesis of architecturally complex heterocyclics caffolds in atom and step economic manner.D epending upon the variety of functionalized al-kynes, this Review is divided into multiple sections. Amongst the vast array of synthetic transformations covered, dearomatizings pirocyclizations and cascades pirocyclization/rearrangementa re of great interest. Synthetic transformations involving the heteroarene-tethered functionalized alkynes with scope, challenges, limitations, mechanism, their application in the total synthesis of natural products and future perceptionsa re surveyed. [a] D. Bag, Prof.
Regioselective benzannulation reaction of indol‐3‐yl‐but‐3‐yn‐2‐ols to functionaly embellished 2‐iodocarbazoles is described for the first time using iodine at room temperature in an open flask. This reaction proceeds through a cascade of 5‐endo spirocyclization, ring‐rearrangement through a vinyl shift, and aromatization in a short time. This protocol offers direct access to uncovered 2‐iodocarbazoles, with a broad substrate scope and good to moderate yields. Further, we have demonstrated the synthetic potential of these compounds using cross‐coupling reactions.
A general electrophilic iodocyclization/nucleophile addition cascade transformation for 1,2-alkynediones for the synthesis of various oxygen heterocycles and access to regioselective alkyne hydroxylation is reported. Furan-tethered ynediones resulted in the construction of exo-enol ethers via carbonyl-alkyne cyclization-initiated heteroarene dearomatization, whereas other (hetero)arene-, alkenyl-, and alkyl-tethered ynediones resulted in the formation of highly functionalized 3(2H)-furanones. Importantly, the developed domino protocols involve the construction of important heterocyclic scaffolds and installation of two functional groups in a single operation. Moreover, the use of water as a nucleophile resulted in regioselective alkyne hydroxylation via furanone ring opening. The developed protocols are characterized by a wide substrate scope, and their utility has been demonstrated by a number of postsynthetic transformations.
The development of novel methodologies for catalytic enantioselective functionalization reactions enabled by chiral transient directing groups is accompanying in a paradigm shift in the field of asymmetric synthesis. In particular, these highly atom-and step-economic enantioinduction processes commonly proceed either via enantioselective CÀ H functionalization, or via enantioselective hydroarylation of the pro-chiral substrates generating point, axial or planar chirality. The use of the transient directing group strategy in CÀ H functionalizations precludes the stoichiometric installations and removal of directing groups and enables efficient, more compatible and economical chemical routes. This minireview highlights asymmetric transition-metal-catalyzed methodologies involving chiral transient directing groups together with the scope, utility and future perspective of the field.
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