Montmorillonite KSF as an Inorganic, Water Stable, and Reusable Catalyst for the Knoevenagel Synthesis of Coumarin-3-carboxylic Acids.

A revision of the Biginelli reaction under solid acid catalysis. Solvent-free synthesis of dihydropyrimidines over montmorillonite KSF

Ru(III)-Catalyzed Cyclization of Arene-Alkene Substrates via Intramolecular Electrophilic Hydroarylation

The generation of a hidden Bronsted acid as a true catalytic species in hydroalkoxylation reactions from metal precatalysts has been clarified in case studies. The mechanism of triflic acid (CF3SO3H or HOTf) generation starting either from AgOTf in 1,2-dichloroethane (DCE) or from a Cp*RuCl2/AgOTf/phosphane combination in toluene has been elucidated. The deliberate and controlled generation of HOTf from AgOTf and cocatalytic amounts of tert-butyl chloride in the cold or from AgOTf in DCE at elevated temperatures results in a hidden Bronsted acid catalyst useful for mechanistic control experiments or for synthetic applications.

Hidden Brønsted Acid Catalysis: Pathways of Accidental or Deliberate Generation of Triflic Acid from Metal Triflates

Catalysis and synthesis are intimately linked in modern organic chemistry. The synthesis of complex molecules is an ever evolving area of science. In many regards, the inherent beauty associated with a synthetic sequence can be linked to a certain combination of the creativity with which a sequence is designed and the overall efficiency with which the ultimate process is performed. In synthesis, as in other endeavors, beauty is very much in the eyes of the beholder.† It is with this in mind that we will attempt to review an area of synthesis that has fascinated us and that we find extraordinarily beautiful, namely the combination of catalysis and sigmatropic rearrangements in consecutive and cascade sequences.

Toward a Symphony of Reactivity: Cascades Involving Catalysis and Sigmatropic Rearrangements

Zeolite-Induced Heterodomino Reaction. Regioselective Synthesis of 2H-1-Benzopyrans from Phenols and α-Alkynols

Chromans 3 and o-isopentenylphenols 4 are synthesi- zed in satisfactory to good yields and selectivities by the reaction of phenols and isoprene in the presence of the commercially available acid faujasite zeolite HSZ-360. The preparation of fine chemicals following environmen- tally friendly strategies represents a challenging goal in the field of synthetic organic chemistry. 1 In the last ten years this approach has had a great development, mainly due to the use of solid acids such as clays and zeolites, (up to that time nearly exclusively employed in petrochemical processes). 2 It is now well stated that the use of these het- erogeneous catalysts represents the best answer both to the new environmental legislation and to the old chemis- try requirements: the processes they promote produce the minimum of pollution and show good 3 yields frequently accompanied by excellent selectivities. As part of a programme designed to develop new selective and preparatively useful methods based on the use of solid acids as catalysts for the preparation of fine chemicals, previous investigations of our laboratory have described the synthesis of 2H-1-benzopyrans from phenols and a- alkynols using a commercial HY-zeolite in typically a het- erogeneously catalyzed process. 4 The a-alkynols, first dehydrate into the corresponding enynes which subsequently react with phenols in a regio- selective way to form 2H-1-benzopyrans; in all cases the sole products arise from interaction of the phenol oxygen with the olefinic double bond and the ortho carbon of the phenol ring with the acetylenic framework of the enyne in- termediate. On the basis of these results we investigated the reaction of isoprene with phenols to produce chromans (3,4-dihydro-2H-1-benzopyrans) over solid acid catalysts. The synthesis of chromans or o-isopentenylphenols (2-(3- methylbut-2-enyl)phenols), 5 important classes of natural and biologically active compounds, has been extensively studied by many researchers, but it's chemo- and regiose- lective control is only achieved by using sophisticated cat- alytic systems such as conveniently prepared acid-base combinations 6 or transition metal complexes, 7 whereas the simple acid catalysis is described to result in less se-

Chiara Muchetti

Papers

Zeolite-Induced Heterodomino Reaction. Regioselective Synthesis of 2H-1-Benzopyrans from Phenols and α-Alkynols

Reaction between Phenols and Isoprene under Zeolite Catalysis. Highly Selective Synthesis of Chromans and o-Isopentenylphenols

Reaction Between Phenols and Isoprene under Zeolite Catalysis. Highly Selective Synthesis of Chromans and o‐Isopentenylphenols.

Zeolite-Induced Heterodomino Reaction. Regioselective Synthesis of 2H-1-Benzopyrans from Phenols and α-Alkynols.