Efficient access to spiro[quinazoline-thiophen](thi)ones via acetic acid mediated [3 + 2] annulation of quinazolin(thi)one enamines with dithianediol

A metal-free approach to the construction of novel spiro[quinazoline-thiophen]one framework via an acetic acid promoted formal [3 + 2] cycloaddition is developed. A library of functionalized spiro[quinazoline-thiophen](thi)ones were efficiently synthesized in good to excellent yields under mild conditions. The protocol features high atom-economy, an eco-benign catalyst and molecular diversity.