Synthesis of Spiro[furan-2,1′-isoindolin]-3′-ones from 2‑(4-Hydroxybut-1-yn-1-yl)benzonitriles and Aryl Aldehydes under the Action of Triflic Acid

The synthesis of spiro­[furan-2,1′-isoindolin]-3′-ones
from 2-(4-hydroxybut-1-yn-1-yl)­benzonitriles and aryl aldehydes is
demonstrated. It involves the initial formation of dihydrofuranylideneisoindolinone
via intramolecular sequential Prins and Ritter reactions, followed
by the ring opening of the furanyl moiety to generate N-acyliminium ions and alcohols for the final cyclization reaction,
and the spiro-cyclic compounds are produced in moderate to good yields.
It is a one-pot, three-component reaction in which one new quaternary
carbon, two five-membered rings, one C–N bond, two C–O
bonds, and one C–C bond are formed. The reaction is carried
out with a Brønsted acid from 0 °C to room temperature within
a short period of time.