Intramolecular Diels–Alder Cycloaddition of Furans (IMDAF) for Natural Product Synthesis

Certain aromatic heterocycles are known to undergo Diels–Alder cycloaddition reactions despite their aromaticity and hence expected decreased reactivity. In particular, the furanyl ring system undergoes ready [4 + 2]-cycloadditions with a variety of dienophiles, such as activated alkenes, alkynes, or allenes. As highlighted in this mini-review, a growing area of interest in organic synthesis involves the use of tethered alkenyl substituted furans for the preparation of many natural products. Cascade reactions proceeding by an intramolecular Diels–Alder cycloaddition are of substantial interest to the synthetic organic community because of the increase in molecular complexity involved and the higher isolated yields when compared to their stepwise counterparts. Central to these syntheses is the use of 2-heterosubstituted furans such as oxy- and aminofurans. The preparation of the robust 2-amido furanyl system makes use of a number of different procedures depending upon the scale and the specific furan desired. Elegant routes to a variety of alkaloid and polyoxygenated natural products have resulted from the basic methodology research on these amido-substituted furans.