An expedient one-pot protocol for the synthesis of functionalized benzofuran containing fused and spiro-heterocycles has been accomplished by the modified Hauser–Kraus (HK) annulation of sulfonylphthalide with o-hydroxychalcones and o-hydroxynitrostyrylisoxazoles. The multicascade process involves Michael addition, Dieckmann cyclization, and a series of cyclizations, eliminations, and rearrangements to deliver the fused and spiro-heterocyclic products. An unusual transformation of fused indenofuran to naphthoquinone, the classical HK adduct, unraveled a novel pathway for the synthesis unsymmetrical naphthoquinones.

An unusual reactivity of 3-sulfonylphthalides with isatylidenemalononitriles has been exploited to provide an efficient entry into 3-sulfonyloxindoles. Although a Hauser-Kraus mechanism can be visualized for the observed transformation, a more probable mechanism, based on control experiments and spectroscopic studies, involves Michael addition of sulfonylphthalide to isatylidenemalononitrile followed by elimination and re-addition of sulfonyl and malononitrile functionalities in an overall functional group exchange between phthalide and oxindolyl moieties. We have also demonstrated the synthetic applications of the sulfonyloxindoles in selected reactions such as conjugate addition and aromatization.

The reactivity of the Hauser−Kraus (H−K) donor, 3-sulfonylphthalide, with various activated imines under basic conditions is demonstrated. The reaction of 3-sulfonylphthalide with Boc-protected aldimine provides a rapid access to 1,2-imine adducts and alkylidenephthalides depending upon the stoichiometry of the base. The alkylidenephthalides could be transformed to ketophthalides, a new class of phthalides, on acid hydrolysis, which upon reductive cyclization using Zn/AcOH afforded the natural product homalicine. On the contrary, the Boc-protected isatinimines undergo an efficient H−K annulation to provide spiroisoquinolinone-oxindoles in excellent yields. However, the corresponding conjugated ketimines afforded Michael adducts, which were converted to the corresponding alkylidenephthalides under TBAF conditions. Article pubs.acs.org/joc

A base-mediated regio- and stereoselective synthesis of functionalized tetrahydro-6H-benzo[c]chromenes and hexahydro-1H,6H-chromeno[6,5-c]chromenone is disclosed here. It involves a [4+2] annulation via cascade double and triple Michael reactions between curcumins and nitrochromenes...

An efficient protocol for the Morita-Baylis-Hillman (MBH) reaction of dicyclopentadienone using CTAB has been developed. The MBH adduct was subsequently transformed to its acetate and bromide derivatives. The 1,3-bielectrophilic character...