Dibenzodioxocine dimer

The geometry of the zwitterions with its exocylic out-of-plane methylene group was quasi-preserved in the recently reported dibenzodioxocine derivative (18) that was formed in rather small amounts by rapidly degrading the NMMO complex at elevated temperatures.45 Strictly speaking, dibenzodioxocine dimer 18 is actually not a dimer of ortho-quinone methide 3, but of its zwitterionic precursor or rotamer 3a (Fig. 6.17). As soon as the out-of-plane methylene group in this intermediate rotates into the ring plane, the o-QM 3 is formed irreversibly and the spiro dimer 9 results... 

In a later extension of the thioacidolysis reaction, a second step, a Raney nickel reduction, was introduced, thereby also permitting the analysis of dimeric and trimeric degradation products by gas chromatography [20,76]. By this method, more than 20 different dimeric and 16 trimeric structures, representing aU the various inter-unit linkages depicted in Fig. 9.5, except the 3-0-4 and dibenzodioxocin structures, have been qualitatively identified from spruce wood. Similar data from birch and aspen wood are also available [23]. 

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