Selective Phosphoranation of Unactivated Alkynes with Phosphonium Cation To Achieve Isoquinoline Synthesis

Diversely functionalized isoquinolines and their core-embedded heterocyclic frameworks: a privileged scaffold for medicinal chemistry

Isoquinoline-enrooted organic small-molecules represent a challenging molecular target in the organic synthesis arsenal attributed to their structural diversity and therapeutic importance. Into the bargain, isoquinolines are significant structural frameworks in modern medicinal chemistry and drug development. Consequently, synthetic organic and medicinal chemists have been intensely interested in efficient synthetic tactics for the sustainable construction of isoquinoline frameworks and their derivatives in enantiopure or racemic forms. This review accentuates an overview of the literature on the modern synthetic approaches exploited in synthesising isoquinolines and their core embedded heterocyclic skeletons from 2021 to 2022. In detail, the methodologies and inspected pharmacological studies for the array of diversely functionalized isoquinolines or their core-embedded heterocyclic/carbocyclic structures involving the introduction of substituents at C-1, C-3, and C-4 carbon and N-2 atom, bond constructions at the C1-N2 atom and C3-N2 atom, and structural scaffolding within isoquinoline compounds have been reviewed. This intensive study highlights the need for and relevance of relatively unexplored bioisosterism employing isoquinoline-based small-molecules in drug design.

Copper-Catalyzed Nitrogen Atom Transfer to Isoquinolines via C-N Triple Bond Cleavage and Three-Component Cyclization

A copper(I)-catalyzed tandem reaction of 2-bromoaryl ketones, terminal alkynes, and CH₃CN is developed, which combines N atom transfer and three-component [3 + 2 + 1] cyclization, and efficiently produces densely functionalized isoquinolines in a facile, highly selective, and general manner. In the reaction, the formation of aromatic C-N bonds along with the complete C-N triple bond cleavage is first realized; Cu(III)-acetylide species might serve as the intermediates, which allow highly selective 6-endo-dig cyclization.

Substituted pyrrolyl-cyanopyridines on the platform of acylethynylpyrroles via their 1 : 2 annulation with acetonitrile under the action of lithium metal

A facile one-pot synthesis of 2-(pyrrolyl)-4-aryl(hetaryl)-5-cyano-6-methylpyridines in 63–87% yield via the cyclization of available acylethynylpyrroles with two molecules of acetonitrile under the action of lithium metal at room temperature has been developed.

The formation of cage phosphoranes and their rearrangements in the reactions of substituted 2-(3-oxo-3-phenyl)ethoxybenzo[d]-1,3,2-dioxaphospholes with perfluorodiacetyl

The Kukhtin-Ramirez reaction of 2-(3-oxo-3-phenyl)ethoxy-benzo[d]-1,3,2-dioxaphospholes with perfluorodiacetyl was monitored by NMR methods. To our surprise the initial stage involved a kinetically controlled [4+4]-cycloaddition with the formation of a cage phosphorane containing a 2',5',8',9'-tetraoxa-2λ⁵-phosphaspiro[benzo[d][1,3,2]dioxaphosphole-2,1'-bicyclo[4.2.1]nonan]-3'-ene (compound 5) scaffold. Intermediate 5 then converts to spirophosphorane-4',5'-bis(trifluoromethyl)-2λ⁵-spiro[benzo[d] [1,3,2]dioxaphosphole-2-yl-2,2'-[1,3,2] dioxaphosphole (compound 4). Compound 4 further rearranges into a cage phosphorane derivative containing a [2,5]epoxybenzo[d][1,3,6,2]trioxaphosphocine] (compound 3) backbone.