For the preparation of 3-alkoxyphthalides from phthalaldehydes and alcohols, a cyclization reaction in the presence of a rhodium(III) catalyst and copper(II) salt is reported. Cyclization of phthalaldehydes also occurs with 1,3-dicarbonyl compounds under similar conditions to produce 3-substituted phthalides in good yields. An acylrhodium(III) species might be a key intermediate in these cyclization
A novel and very short synthesis of the useful title hydrocarbon 2 is presented. Its key step is based on a Diels-Alder reaction of isobenzofuran 4. The lithium salt of 2 gives a remarkably stable valenceisomer of anthracene 1 in a reaction analogous to the indene → benzobenzvalene transformation.
It is demonstrated for the first time that carboxylic ortho esters may be reduced to acetals using hydrogen as the reducing agent. Hydrogenolysis was performed under mild conditions over commercially available hydrogenation catalysts (5% Pd/C and 5% Pt/C). The present method is especially useful for the selective transformation of carboxylic acids and lactones into acetals.
An approach for partial oxygenation through a carbocation as an intermediate was successfully developed by using nitric oxide under the influence of N-hydroxyphthalimide. Thus, a variety of benzylic ethers were converted into the corresponding partially oxidized compounds, which are difficult to prepare by conventional methods, in high yields. For example, the reaction of phthalane with NO in the presence of a catalytic amount of NHPI at 60 degrees C gave phthalaldehyde in 80% yield. The reaction was found to proceed through the formation of a hemiacetal, such as 1-hydroxyphthalane. In addition, 1,3-di-tert-butoxymethyl benzene afforded 1,3-benzenedicarbaldehyde in good yield. On the other hand, isochroman was converted into 1,1'-oxodiisochromane under these reaction conditions. The reaction of ethers with NO in the presence of a NHPI catalyst is thought to proceed via the formation of a carbocation as an intermediate. A possible reaction path was suggested.
Benzo[f]isobenzofuran. Mechanistic aspects of isobenzofuran formation from acetals and ortho esters