A Novel Oxidative Intramolecular (4+2)Cycloaddition of Silylene-Protected Dihydroxystyrene Derivatives Leading to peri-Hydroxy Polycyclic Aromatic Compounds: A Synthesis of the ABCD Ring.
Under a catalytic amount of PTSA in aqueous or alcoholic media, activated unsymmetrical arylalkynes 1 undergo regioselective water or alcohol addition to afford successfully carbonyl compounds 2 in good to excellent yields. This new environmentally metal-free procedure, which afforded only Markovnikov adducts, is characterized by the mildness of acidic conditions and the excellent regio- and chemoselectivity
A novel intramolecular [4+2] cycloaddition of silylene protecting dihydroxystyrene derivatives: A versatile synthesis of linearly condensed -hydroxy aromatic compounds
The first example of an intramolecular [4+2] cycloaddition of the silylene protecting dihydroxystyrene derivatives leading to linearly condensed -hydroxy aromatic compounds (6a–c) is described.
p-Toluenesulfonic acid-promoted selective functionalization of unsymmetrical arylalkynes: a regioselective access to various arylketones and heterocycles
Regioselective hydration of a wide range of internalalkynes has been afforded in high to good yields by using PTSA in EtOH. The scope of the reaction of alkynes has been delineated. Arylaliphatic alkynes and diarylalkynes were regioselectively hydrated in good to excellent yields and short reaction times when the reaction was achieved under microwave irradiation. Moreover, diarylalkynes, arylenynes
A Novel Oxidative Intramolecular (4+2)Cycloaddition of Silylene-Protected Dihydroxystyrene Derivatives Leading to peri-Hydroxy Polycyclic Aromatic Compounds: A Synthesis of the ABCD Ring.
Heating of the silylene protected dihydroxystyrene generated from the O-hydroxyacetophenone (3a) at 130-150°C for 15-48h in a sealed tube gave intramolecular [4+2]cycloaddition products (5 and 6). The addition of chloranil to the reaction mixture brought about an oxidative intramolecular [4+2]cycloaddition to give the linearly condensed peri-hydroxy aromatic compound(7a) in excellent yield. The generality of this cycloaddition and application to a short and efficient synthesis of the ABCD ring system of fredericamycin A are described.