Synthesis and tautomeric studies of 1-benzylisobenzofuran and related compounds

Preparation of phenalenes and hydronaphthacenes through tandem alkyne Fischer–carbene complex coupling and inter- or intra-molecular Diels–Alder reactions

“…17 If a sequential addition involving (1) reaction of the carbene complex and alkyne at 100 °C for 1 h and (2) addition of DMAD was employed, a surprisingly excellent yield of phenalene-containing product 11 was observed after silica gel purification. Initially, an efficient process was not anticipated under these conditions since isobenzofurans bearing α-hydrogens are unstable with respect to conversion to alkylidenephthalans, 18 and success thus requires this critical intermediate to survive intact for more than an hour at 100 °C. Naphthalene 11 can in theory be obtained using the N,N -dimethylhydrazone derivative of ketone 1 , 19 however this process was considerably less efficient.…”

Benz[f]isoindole

“…As expected, thermal decomposition of 2-naphthalenedi- (10), which reacted with 1 -(phenylmethyl)pyrrole to afford adduct 11. Hydrogenation of imine 11 in methanol in the presence of 10% palladium-charcoal gave ll-(phenylmethyl)-l,2,3,4-tetrahydroanthracen-l,4-imine (12). An attempt to convert 12 to compound 9 by selective hydrogenolysis failed; only 1,2,3,4-tetrahydroanthracene and benzylamine were recovered.…”

“…This decrease presumably results from the inability of the nitrogen-substituted isoindoles to tautomerize to a benzenoid (isoindolenine) form, which would display a greater tendency to polymerize.8•10'13 Prompted by our success with flash vacuum thermolysis as a technique for the preparation of isoindoles,5'6 it was of interest to apply this method to the synthesis of 2-(phenylmethyl)benz[/]isoindole (15), whose precursor 12 was already in hand as noted above. Accordingly, 11 -(phenylmethyl)l,2,3,4-tetrahydroanthracen-l,4-imine (12) was pyrolyzed under the usual conditions. Surprisingly, none of the expected 2 -(phenylmethyl) benz [/] isoindole (15) was detected.…”

“…

A new class of nitrogen-bridged anthracenes has been prepared by reaction of 1 -(phenylmethyl)pyrrole and also tert -butyl pyrrole-1-carboxylate with 2,3-didehydronaphthalene (10) to give ll-(phenylmethyl)-l,4-dihydroanthracen-l,4-imine (11) and tert-butyl 1,4-dihydroanthracen-1,4-imine-11-carboxylate (13), respectively. Hydrogenation of 11 provides ll-(phenylmethyl)-l,2,3,4-tetrahydroanthracen-l,4-imine (12), which on hydrogenolysis yields 1,2,3,4-tetrahydroanthracene. Hydrogenation of 13 followed by acidic cleavage of the iert -butyloxycarbonyl group affords l,2,3,4-tetrahydroanthracen-l,4-imine (9), which yields benz[/]isoindole (3 <=± 5) on retro-Diels-Alder thermolysis.

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Reactions of phthalans with dienophiles. II. Synthesis of naphthalenes and dihydronaphthalenes by reaction of ethyl maleate and maleic anhydride with 1,1-diethoxyphthalan

“…Whereas Kende er al. (4), Wiersum and Mijs (5), and Chacko et al (6) have observed the predominance of endo isomers in these reactions, Hamaguchi and Ibata (7) found an endo-exo ratio of 1: 1 in adducts that they prepared. In all cases, the endo-exo ratio was determined by nrnr spectral analysis.…”