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.

scholarly journals Tandem methodology for heterocyclic synthesis

2004 ◽  
Vol 76 (11) ◽  
pp. 1933-1952 ◽  
Author(s):  
A. Padwa
Keyword(s):  
Diels Alder ◽  
Synthetic Method ◽  
Heterocyclic Synthesis ◽  
Pummerer Reaction ◽  
Powerful Approach ◽  
Target Molecules ◽  
Alpha Beta ◽  
Molecular Complexity ◽  
Complex Target ◽  
Substituted Furans

Tandem methodology for heterocyclic synthesis represents a powerful approach for the rapid buildup of molecular complexity from potentially simple starting materials. Work from our laboratory has shown that the rhodium(II)-catalyzed cyclization cascade of alpha-diazo imides represents an effective method for the synthesis of a variety of heterocyclic systems. As an extension of these studies, 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. Alpha-thiocarbocations generated from the Pummerer reaction of beta-phenylsulfinylmethyl-alpha, beta-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. Application of the process for the preparation of the stenoma alkaloid stenine was recently carried out in our laboratory.

Intramolecular Diels–Alder Reactions of Oxazoles, Imidazoles, and Thiazoles

Synthesis ◽  
2020 ◽  
Author(s):  
Peter Wipf ◽  
Thanh T. Nguyen
Keyword(s):  
Natural Products ◽  
Lewis Acid ◽  
Acid Catalysis ◽  
Copper Catalysts ◽  
Diels Alder ◽  
Synthetic Approach ◽  
Highly Efficient ◽  
Intramolecular Cycloadditions ◽  
Western Segment ◽  
Target Molecules

AbstractThe development of the intramolecular Diels–Alder cycloaddition­ of azole heterocycles, i.e. oxazoles (IMDAO), imidazoles (IMDAI), and thiazoles (IMDAT), has had a significant impact on the efficient preparation of heterocyclic intermediates and natural products. In particular, highly efficient and versatile IMDAO reactions have been utilized as a key step in several synthetic schemes to provide alkaloids and terpenoid target molecules. More limited studies have been performed on IMDAI and IMDAT cycloadditions. Some drawbacks, such as the occasionally­ challenging preparation of IMDA precursors, are also highlighted in this review. Perspectives are provided on how IMDAI and IMDAT­ transformations can be further expanded for target-directed syntheses.1 Introduction2 Oxazoles2.1 IMDAO Approaches to Furanosesquiterpenes and Furanosteroids2.1.1 Syntheses of Highly Oxygenated Sesquiterpenes2.1.2 Syntheses of (±)-Gnididione and (±)-Isognididione2.1.3 Synthesis of (±)-Stemoamide2.1.4 Synthesis of (±)-Paniculide A2.1.5 Syntheses of (+)- and (–)-Norsecurinine2.1.6 Synthesis of Evodone2.1.7 Syntheses of (±)-Ligularone and (±)-Petasalbine2.1.8 Syntheses of Imerubrine, Isoimerubrine, and Grandirubrine2.1.9 Syntheses of Furanosteroids2.1.10 Syntheses of Substituted Indolines and Tetrahydroquinolines2.2 IMDAO Approaches to Pyridines: the Kondrat’eva Reaction2.2.1 Syntheses of Suaveoline and Norsuaveoline2.2.2 Synthesis of Eupolauramine2.2.3 Syntheses of (–)-Plectrodorine and (+)-Oxerine2.2.4 Synthesis of Amphimedine2.2.5 Synthetic Approach to the Western Segment of Haplophytine2.2.6 Synthesis of Marinoquinoline A2.2.6.1 IMDAO Approach to Marinoquinoline A2.2.6.2 Scope of Allenyl IMDAO Cycloaddition2.3 Lewis Acid Catalysis in IMDAO Reactions2.3.1 Effects of Europium Catalysts on IMDAO Reactions2.3.2 Effects of Copper Catalysts on IMDAO Reactions3 Imidazoles 4 Thiazoles4.1 Syntheses of Menthane and Eremophilane4.2 Further Comments on the Intramolecular Cycloadditions of Thiocarbonyl Ylides5 Conclusions and Outlook

4-Aryl-3-substituted Furans

1994 ◽  
Vol 59 (12) ◽  
pp. 2721-2726 ◽  
Author(s):  
Jarmila Štetinová ◽  
Ján Leško ◽  
Miloslava Dandárová ◽  
Rudolf Kada ◽  
Roman Koreň
Keyword(s):  
Thermal Decomposition ◽  
Triple Bond ◽  
Alder Reaction ◽  
Diels Alder ◽  
Diels Alder Reaction ◽  
Substituted Furans

4-Aryl-3-substituted furans IIIa - IIId were prepared by Diels Alder reaction of 4-phenyloxazole (I) with compounds IIa - IId, containing an activated triple bond, and subsequent thermal decomposition of the cycloadduct.

Diels−Alder Reaction of 2-Amino-Substituted Furans as a Method for Preparing Substituted Anilines

1997 ◽  
Vol 62 (12) ◽  
pp. 4088-4096 ◽  
Author(s):  
Albert Padwa ◽  
Martin Dimitroff ◽  
Alex G. Waterson ◽  
Tianhua Wu
Keyword(s):  
Alder Reaction ◽  
Diels Alder ◽  
Substituted Anilines ◽  
Diels Alder Reaction ◽  
Substituted Furans

scholarly journals Exploiting the borono-Mannich reaction in bioactive alkaloid synthesis

2008 ◽  
Vol 80 (4) ◽  
pp. 751-762 ◽  
Author(s):  
Stephen G. Pyne ◽  
Christopher W. G. Au ◽  
Andrew S. Davis ◽  
Ian R. Morgan ◽  
Thunwadee Ritthiwigrom ◽  
...  
Keyword(s):  
Mannich Reaction ◽  
Amino Alcohols ◽  
Core Structure ◽  
Indolizidine Alkaloids ◽  
Acyliminium Ions ◽  
Alkaloid Synthesis

We have demonstrated that the borono-Mannich reaction is a versatile and efficient reaction for the diastereoselective preparation of chiral 1,2-amino alcohols. These Mannich products are valuable starting materials as shown in this report by the synthesis of bioactive polyhydroxylated pyrrolizidine and indolizidine alkaloids. Initial studies, directed at the more complex Stemona alkaloids and using the borono-Mannich reaction on cyclic N-acyliminium ions, are encouraging, as demonstrated by the synthesis of the pyrido[1,2-a]azepine core structure of stemocurtisinol.

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