Abstract
The 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 Introduction
2 Oxazoles
2.1 IMDAO Approaches to Furanosesquiterpenes and Furanosteroids
2.1.1 Syntheses of Highly Oxygenated Sesquiterpenes
2.1.2 Syntheses of (±)-Gnididione and (±)-Isognididione
2.1.3 Synthesis of (±)-Stemoamide
2.1.4 Synthesis of (±)-Paniculide A
2.1.5 Syntheses of (+)- and (–)-Norsecurinine
2.1.6 Synthesis of Evodone
2.1.7 Syntheses of (±)-Ligularone and (±)-Petasalbine
2.1.8 Syntheses of Imerubrine, Isoimerubrine, and Grandirubrine
2.1.9 Syntheses of Furanosteroids
2.1.10 Syntheses of Substituted Indolines and Tetrahydroquinolines
2.2 IMDAO Approaches to Pyridines: the Kondrat’eva Reaction
2.2.1 Syntheses of Suaveoline and Norsuaveoline
2.2.2 Synthesis of Eupolauramine
2.2.3 Syntheses of (–)-Plectrodorine and (+)-Oxerine
2.2.4 Synthesis of Amphimedine
2.2.5 Synthetic Approach to the Western Segment of Haplophytine
2.2.6 Synthesis of Marinoquinoline A
2.2.6.1 IMDAO Approach to Marinoquinoline A
2.2.6.2 Scope of Allenyl IMDAO Cycloaddition
2.3 Lewis Acid Catalysis in IMDAO Reactions
2.3.1 Effects of Europium Catalysts on IMDAO Reactions
2.3.2 Effects of Copper Catalysts on IMDAO Reactions
3 Imidazoles
4 Thiazoles
4.1 Syntheses of Menthane and Eremophilane
4.2 Further Comments on the Intramolecular Cycloadditions of Thiocarbonyl Ylides
5 Conclusions and Outlook
Key words
oxazole - pyridine - intramolecular Diels–Alder - [4+2] cycloaddition - Kondrat’eva
reaction - total synthesis of natural products - fused heterocycles
