Furan ring oxidative degradation

Methanolysis of 199, followed by oxidative degradation of the furan ring proceeded smoothly, providing KDO derivative 66. Transformation of 199 into 2-deoxy-KDO required the hydrogenation in the first step leading after several transformation to the methyl ester of the resulted acid. 

Cleavage of N, N -diaUcylhydrazides. Mild conditions are involved in this cleavage method. The furan ring in a substrate is not degraded by the oxidant. 

Confirmation of the isoprenoid nature of the furan rings of dictamnine (328) and of N-methylplatydesminium salt (326) in S. japonica was provided indirectly by Grundon and his co-workers (224), who showed that the 3-prenylquinolones 321 and 322 labeled at - with 14C were good precursors of both alkaloids (3.6-4.8% incorporation). Specific incorporation of the precursors into dictamnine was indicated by oxidative degradation by a method similar to that used previously. N-Methylplatydesminium salt was counted as its base-cleavage product edulinine (256), which was converted into isodictamnine (Section IV,B,3) oxidation via 3-carboxy-4-hydroxy-l-methyl-2-quinolone gave 14C-labeIed carbon dioxide. 

The most common form of heterocyclic oxygen is in furan ring systems. Substituted furan rings have been reported in coal extracts, pyrolysis tars, and oxidative degradation products (Duty et al., 1980 Bodzek and Marzek, 1981 see also White, 1983). However, to exactly what extent the diben-zofuran system exists in the parent coal is not clear. The isolation of dibenzofuran from oxidative degradation products and low-C temperature coal extracts supports the view that it is present in the parent coal. 

Ring contraction of coumarins is used for the preparation of benzo[Z>]furans. Alkaline degradation of the 3-halo-, 4-halo- or 3,4-dihalo-coumarins gives the coumarilic acids (Scheme 104). The coumarilic acids are decarboxylated to the corresponding benzo[Z> ]f urans. Basic mercury(II) oxide oxidation of 4-phenylcoumarin (neoflavanoid) yields the 3-phenyl-benzo[/>]furan (71IJC1316). 

Ring contraction was also noted on acetolysis of 3-tosyltetra-O- methyl-(+)-catechin the 2,3-dihydrobenzo[Z> ]furan formed can be oxidized to the benzo[f>]furan (Scheme 105) (66JCS(C)634). The 2-phenylbenzo[6]furan and its 2,3-dihydro derivative are degradation products of lignin and as such have been investigated extensively. 

The difficult translation of SOMO activation to cyclic ketones was achieved with the help of catalyst 6, which was developed earUer for Diels-Alder reactions of cyclic ketones via iminium activation. The difficulty Hes in the fact that aldehydes and ketones exhibit largely different steric and electronic properties with respect to catalyst interactions [16]. Competitive catalyst degradation under the oxidative conditions (i.e., oxidation of the methyl group attached to furan) was circumvented by transforming the methyl into a trifluoromethyl group, or by direct replacement of the furyl ring with less electron-rich heteroaryl systems such as benzofuran (8) or benzothiophene (9), which are less sensitive to oxidation (Scheme 39.5). 

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