Dibenzodioxocin

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... 

FIGURE 12.5 In situ generation of quinone methides to produce dibenzodioxocin model compounds. (See text for details.)... 

Karhunen, P Rummakko, P. Pajunen, A. Brunow, G. Synthesis and crystal structure determination of model compounds for the dibenzodioxocine structure occurring in wood lignins. J. Chem. Soc., Perkin Trans. 1996, 1, 2303-2308. 

Karhunen, P Rummakko, P. Sipila, J. Brunow, G. Kilpelainen, I. The formation of dibenzodioxocin structures by oxidative coupling. A model reaction for lignin biosynthesis. Tetrahedron Lett. 1995, 36, 4501 4504. 

Unsubstituted dibenzodioxocin 295g (R = R1 = H, X = CH2) was brominated with NBS to give the corresponding monobromo derivative 295h (R = R1 = H, X = CHBr) in low yield <2000W023417>. 

Flash vacuum pyrolysis of the dibenzodioxocine 6 was reported to give the 2-(2 -hydroxybenzyl)benzaldehyde 178 (Equation 39), presumably via the intermediate diradical formation <1995JOC8410>. 

Intermolecular condensation with the formation of two C-O bonds is a viable approach to the benzo-annelated dioxocines (cf. 1996CHEC-II(9)527). Treatment of catechol with a,a -xylene dichloride afforded dihydrodi-benzo[, /][l,4]dioxocine 6 (an oil) in excellent yield (Scheme 19) <1995JOC8410>. Similarly, catechol reacted with l,2,4,5-tetrakis(bromomethyl)benzene to form the dibenzodioxocine 182 (m.p. 87-89 °C) in moderate yield <2001H(54)849, 2001T8667>. The dibromide 182 was further treated with phenanthrenequinone under reductive conditions to afford 9,13,18,22-tetraoxa-9,10,12,13,18,19,21,22-octahydrobenzo-9, 10 -phenanthro[i / ]benzo[l,2- 4,5- ]dicyclooctene 151 <2001T8667>. Catechol reacted with dibromoethane under phase-transfer catalysis conditions to form tetrahydro-l,6-benzodioxocine 183 in high yield <2001SC1>. 

Biomimetic synthesis of model compounds for dibenzodioxocines occurring in wood lignins was carried out, as follows. On oxidation with Ag20 in CH2CI2 (room temp., 45 h), the reaction of dehydrodipropylguaiacol (786) with coniferyl alcohol (298) provided... 

Dibenzo-/ -dioxins 1086 Dibenzodioxocines 1308, 1309, 1311 Dibenzofurans, formation of 1289, 1291 Dibenzopyranones, formation of 1257 Dibenzoylmethane enol, IR spectrum of 382... 

Diode array-UVD (DA-UVD) 953 1,3,2-Dioxaborins, formation of 683 Dioxanes—see 1,3-Benzodioxanes Dioxepens—see Dibenzodioxepens Dioxins—see Dibenzo-p-dioxins Dioxiranes, as oxidants 1255, 1257, 1258 Dioxocines—see Dibenzodioxocines Dioxygen-copper complexes, as oxidants 1194, 1198... 

FIGURE 3.5 Biphenyl units bonded as dibenzodioxocin structures. 

P Karhunen, P Rummakko, J Sipila, G Brunow, and I Kilpelainen. The Formation of Dibenzodioxocin Structures by Oxidative Coupling A Model Reaction for Lignin Biosynthesis. Tetrahedron Lett. 36 4501 504, 1995. 

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