Coumarans

Coumaran-2,3-semidione was prepared by treatment of eoumaran-2,3-dione with the enolate anion of propiophenone in DMSO (70JA2762). 

Naphtho[2,l-6]furo[2,3-c][l,2,4]triazines 198 were prepared (88JHC-1117) by the reaction of 4-5-benzocoumaran-2,3-dione with thiosemicar-bazide to give 195, whose ethylation in the presence of sodium hydroxide gave 197 via 196. Reaction of 197 with aniline gave 198 via the first displacement of the ethylthio group whose product could be isolated with a shorter reaction time. On the other hand, the similar sequence of reactions on coumaran-2,3-diones differs markedly from that of 4,5-benzocoumaran-2,3-diones, where the cyclization of 195 to 198 could not be effected. The behavior of the later dione resembles that of isatin and thianaphthenequinone (Scheme 41). 

Coumaran-3-one without substitution at the 2-position can be synthesized by oxidation of silyl enol ether 62 with iodosobenzene under Lewis acid conditions. a-Hydroxyketone 63 is formed as a side product (86SC1239). 

Various authors have also described the reduction of dimeric lignin model structures both aromatic aldehydes and aromatic acids were reduced by ligninolytic cultures of P. chrysosporium, sis shown by the reduction of the 0-0-4 model 1 (acid, lacking the C7-substituent) to the corresponding alcohol 2 (24) and the phenyl coumaran models 3 (acid) and 4 (aldehyde) to the corresponding alcohol 5 (25). 

For the present discussion, a number of these conversions are of relevance. Phenolic dimeric model compounds of the 0-1, 0-0-4 and phenyl coumaran type are degraded via Ca-arene cleavage yielding methoxy-... 

Coumalyl chloride reactions, 3, 691 Coumaphos against ectoparasites veterinary use, 1, 217 Coumaranone H NMR, 4, 579 synthesis, 3, 849-850 Coumaran-2-ones, 4, 579 IR spectra, 4, 590 reactions, 4, 649 structure, 4, 552 synthesis, 4, 128... 

The 2-allylphenols in the presence of add catalysts such as pyridine hydrochloride, -66 hydrobromic add-acetic add, or formic acid86 form 2-methyldihydrobenzofurans (coumarans) such as LXYI. In the pres-... 

The quinone methides can also react by elimination of formaldehyde or hydrogen ion at the /3-carbon atom, especially when the formation of conjugated diaryl structures is possible. Examples of this type of reactions are the formation of stilbenes from phenyl coumarans or 1,2-diarylpropane struc-... 

Fig. 7-13. Reaction of phenyl coumaran structures during neutral sulfite pulping (see Gel-lerstedt, 1976).

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