Metallafurans and their synthetic chemistry

Based on isolobal analogy, the definition of metallafuran was described and its synthetic chemistry was briefly summarized. In the structure of furan, when one of CH groups was replaced by an isolobal metal fragment MLn (M = metal; L = ligand), the corresponding organometallic complex was called metallafuran, which should be two possible isomers called α-metallafuran (metal fragment at α-carbon of original furan) and β-metallafuran (metal fragment at β-carbon of original furan). As an organometallic complex, α-metallafuran has two resonant forms: one can be viewed as carbonyl coordinated vinyl metal complex and the other can be viewed as alkoxymetal carbene. Therefore, α-metallafuran was also called chelated vinyl ketone metal complex or oxametallacyclopentadiene in the early literatures. For synthesis of metallafurans, α-metallafurans were very common and easily prepared, for example, from alkynes insertion into acyl metal complexes and so on. While there were rare examples reported for β-metallafurans. In this mini review, the synthetic chemistry of metallafuran was mainly focused on its formation mechanism.