ChemInform Abstract: π-Cyclization Reactions of Thio N-Acyliminium Ions for Heterocyclic Synthesis.

ChemInform ◽  
2010 ◽  
Vol 29 (39) ◽  
pp. no-no
Author(s):  
S. M. SHEEHAN ◽  
L. S. BEALL ◽  
A. PADWA
Keyword(s):  
Heterocyclic Synthesis ◽  
Cyclization Reactions ◽  
Acyliminium Ions

π-Cyclization reactions of thio N-acyliminium ions for heterocyclic synthesis

1998 ◽  
Vol 39 (27) ◽  
pp. 4761-4764 ◽  
Author(s):  
Scott M. Sheehan ◽  
L. Scott Beall ◽  
Albert Padwa
Keyword(s):  
Heterocyclic Synthesis ◽  
Cyclization Reactions ◽  
Acyliminium Ions

Application of cascade processes toward heterocyclic synthesis

2003 ◽  
Vol 75 (1) ◽  
pp. 47-62 ◽  
Author(s):  
A. Padwa
Keyword(s):  
Diels Alder ◽  
Heterocyclic Synthesis ◽  
Widespread Application ◽  
Pummerer Reaction ◽  
Acyliminium Ions ◽  
Alkaloid Synthesis ◽  
Cascade Processes ◽  
Target Molecules ◽  
Complex Target ◽  
Substituted Furans

The reactions of N-acyliminium ions with tethered π-bonds are among the most important methods for preparing complex nitrogen-containing heterocycles. Pummerer-based cyclizations are also finding widespread application in both carbo- and heterocyclic syntheses. As part of a program concerned with new methods for alkaloid synthesis, we became interested in using a linked Pummerer/N-acyliminium ion cyclization sequence since we felt that this combination offers unique opportunities for the assemblage of complex target molecules. A synthetic method that combines transformations of different reaction types significantly broadens the scope of such procedures in synthetic chemistry. α-Thiocarbocations generated from the Pummerer reaction of β-phenylsulfinylmethyl-α,β-unsaturated amides can be intercepted by the adjacent amido group to produce transient amino- substituted furans, which undergo subsequent Diels-Alder cycloadditions. Using this domino amido-Pummerer/Diels-Alder cascade, we were able to assemble novel polycyclic systems in a single operation. The key step in the process involves the generation of a reactive N-acyliminium ion by fragmentation of an amino-substituted [4+2] cycloadduct. The successful synthesis of a number of alkaloids by this sequence of reactions reveals the usefulness and importance of this unique domino cascade.

Mechanistic Study and Development of Catalytic Reactions of Sm(II)

2018 ◽  
Author(s):  
Sandepan Maity ◽  
Robert Flowers
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Proton Donor ◽  
Catalytic Reactions ◽  
Mechanistic Study ◽  
Mechanistic Studies ◽  
Cyclization Reactions ◽  
Mechanistic Approach ◽  
Donor Source

Despite the broad utility and application of SmI<sub>2</sub>in synthesis, the reagent is used in stoichiometric amounts and has a high molecular weight, resulting in a large amount of material being used for reactions requiring one or more equivalents of electrons. We report mechanistic studies on catalytic reactions of Sm(II) employing a terminal magnesium reductant and trimethyl silyl chloride in concert with a non-coordinating proton donor source. Reactions using this approach permitted reductions with as little as 1 mol% Sm. The mechanistic approach enabled catalysis employing HMPA as a ligand, facilitating the development of catalytic Sm(II) 5-<i>exo</i>-<i>trig </i>ketyl olefin cyclization reactions.

Utility of Ethylidenethiosemicarbazides in Heterocyclic Synthesis

2016 ◽  
Vol 14 (1) ◽  
pp. 3-21 ◽  
Author(s):  
Sayed M. Riyadh ◽  
Sobhi M. Gomha ◽  
Elmahdi A. Mahmmoud
Keyword(s):  
Heterocyclic Synthesis
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