NXS, Morpholine, and HFIP: The Ideal Combination for Biomimetic Haliranium-Induced Polyene Cyclizations

In
contrast to Nature that accomplishes polyene cyclizations seemingly
with ease, such transformations are difficult to conduct in the lab.
In our program dealing with the development of selective halogenations
of alkenes, we now asserted that standard X+ reagents are
perfectly suited for the biomimetic cation-π cyclization of
both electron rich and poor linear polyenes in the presence of the
Lewis base morpholine and the Lewis acid HFIP. The method stands out
due to its broad substrate scope and practicability together with
high chemical yields and excellent selectivities, even for highly
challenging chloriranium-induced polyene cyclizations.