Synthesis, structure, and spectral and photochemical properties of fulgides of the indole series with an adamantylidene fragment

New fulgides of the indole series with adamantylidene fragments were synthesized: 3-(adamant-2-ylidene)-2-[1'-(3'-indolylethylidene)]succinic anhydride (1) and 3-(adamant-2-ylidene)-2-(3'-indolylmethylene)]succinic anhydride (2). By means of electronic absorption and H-1 NMR spectroscopy and X-ray diffraction analysis, fulgides 1 and 2 were shown to have Z- and E-configurations, respectively. The photochemical properties of 1 and 2 were studied. It was shown that along with Z-E photoisomerization of these compounds, in solution they undergo a cyclization reaction to yield a colored photoproduct. Specific structural features of fulgide 1 affecting its photochemical properties were discussed. The introduction of a bulky adamantylidene group decreases the extent of the conversion of compound 1 into cyclic isomer C.