Recently we have reported the formation and the trapping of 4,5-dehydrotropone (I) 1) as a novel reactive species. Taking into account the wide applicability of dehydroarenes (arynes) in organic synthesis, 2) the dehydrotropone will be possibly of a potential and useful intermediate for the synthesis of new bridged troponoids which could hardly be derived by other known methods.
From this point of view, it is of interest to examine the reactivity and the synthetic utility of 1.
As a part of this program, we wish to communicate the reaction of 1 with typical 1,3-dienes, cyclopentadiene and cyclohexa-1,3-diene, and some of the spectroscopic properties of the tropone and 8,8_dicyanoheptafulvene incorporated in bicyclo[2.2.l]heptane and bicyclo[2.2.2loctane ring systems being derived by the above reaction.
In the presence of a large excess of cyclopentadiene or cyclohexa-1,3-diene, a mixture of l-amino_lH-and2 -amino-2H-cycloheptatriazol-6-one (3--1:l) 1) was reacted with lead tetraacetate in dry methylene chloride at room temperature under nitrogen.
After usual work-up, the products were isolated using basic alumina chromatography (CH2C12) to give the desired 1,4-adducts, 1,4-dihydro-1,4-methano-7H-benzocyclohepten-7-one (2) as pale yellow oil 3, (-50%) or 1,4-dihydro-1,4ethano-7H-benzocyclohepten-7-one (3) as colorless needles of mp 82-84Β°C (45%),
respectively.
The structural assignments follow elemental analyses 4: and the spectral data shown in Table 1.
Tropones, 2, 3, exist in trifluoroacetic acid as hydroxytropylium ion form, 569