Recently, the intramolecular electrophilic cyclization of nucleophiles, such as oxygen, nitrogen, sulfur, phosphorus, and also sp2 or sp3 hybridized carbon, with alkynes has proven to be an effective method for the synthesis of carbocyclic and heterocyclic compounds. Many important heterocycles and carbocycles have been accessed using this protocol. However, the electrophilic carbocyclization with allenes has often been considered to be less attractive due to the lack of efficient control of the regio- and stereoselectivity. Not long ago, Barluenga and co-workers reported an interesting carbocyclization of allenes to halogenated dihydronaphthalene in the presence of electrophiles. But the use of expensive I(py)2BF4, and the relatively low temperature make this approach a bit limited synthetically.
Researchers of Lanzhou University and Lanzhou Institute of Chemical Physics (LICP) of the CAS have developed an efficient synthesis of substituted dihalogenated 1H-indenes, dihydronaphthalenes, and dihydrobenzo[b]oxepines in moderate yields from simple aryl propargylic alcohols under mild reaction conditions has been developed. The dihalogenated moiety can be readily introduced into the carbocycle and heterocycle in a position not easily obtained previously. The resulting diiodinated products can be used to prepare more complex products by using known organopalladium chemistry. In this reaction, both halogen atoms, such as I and Br, are used effectively and trace amounts of water are necessary. Further studies on electrophilic cyclizations of propargylic alcohols are in progress in the laboratory.
The work has received support from the National Science Foundation and National Basic Research Program of China. The findings have been published in Org. Lett. (Org. Lett., Vol. 13, No. 4, 2011).
Org. Lett. Paper
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