Isoquinoline, 3-methoxy-, formation

Moreover, one should mention that in spite of similar electronic structures, PBN and the isoquinoline nitrone (278) react in a different way. Under no circumstances does PBN give an oxidative methoxylation product, whereas nitrone (278) reacts readily to form a,a-dialkoxy-substituted nitroxyl radical (280) (517). Perhaps this difference might be due to the ability to form a complex with methanol in aldo-nitrones with -configuration. This seems favorable for a fast nucleophilic addition of methanol to the radical cation (RC), formed in the oxidation step. The a-methoxy nitrone (279), obtained in the initial methoxylation, has a lower oxidation potential than the initial aldo-nitrone (see Section 2.4). Its oxidation to the radical cation and subsequent reaction with methanol results in the formation of the a,a-dimethoxy-substituted nitroxyl radical (280) (Scheme 2.105). 

The photoamination of t-S having a methyl or chloro group in the para position or a methoxy group in the meta or ortho positions gave non-selective adducts. Irradiation of the primary aminoethyl and aminopropylstilbenes in acetonitrile-water solution in the presence of DCNB results in the formation of isoquinoline and benzazepine products in good preparative yields24,28 (equations 45 and 46). The preparation of benzazepine represents an improvement in overall yield when compared to previously reported non-photochemical synthetic routes. 

Photocyclization of an enamide (review [2S9S]) containing a methoxy group leads to the formation of a pyridinone ring of an intermediate in the synthesis of (— )-sincitine. Reviews of numerous syntheses of isoquinoline alkaloids [2487] and of the use of Reissert compounds in such syntheses [2488] are available. 

Oxidation of codamine ethyl ether (LXVI) cleaved the benzylisoquinoline system to 4-methoxy-5-ethoxyphthalic acid (LXVH) and veratric acid (VT). While the formation of these two acids precluded the location of the phenolic hydroxyl in the benzyl residue, LXVTI could have arisen from either a 6- or 7-ethoxy-substituted isoquinoline system. This question was settled by repeating the potassium permanganate oxidation of 0.0085 g. of codamine ethyl ether (LXVI) under gentle conditions. This time, 1-ke-to-2-methyl-6-methoxy-7-ethoxy-l, 2,3,4-tetrahydroisoquinoline (LXVIII) was isolated its structure was confirmed by synthesis, and therefore codamine is XXII. 

The ET-sensitized photoamination of 1,1-diarylethylenes with ammonia and most primary amines yields the anti-Markovnikov adducts. Photoamination of unsymmetrically substituted stil-benes yields mixtures of regioisomers 15 and 16. Modest re-gioselectivity is observed for p-methyl or p-chloro substituents however, highly selective formation of adduct 15 is observed for the p-methoxy substituent (Table 5). Selective formation of 15 was attributed to the effect of the methoxy substituent on the charge distribution in the stilbene cation radical. This re-gioselectivity has been exploited in the synthesis of intermediates in the preparation of isoquinolines and other alkaloids." Photoamination of 1-phenyl-3,4-dihydronaphthalene yields a mixture of syn and anti adducts 17 and 18 (Scheme 5)." Use of bulky primary amines favors formation of the syn adduct (Table 5), presumably as a consequence of selective anti protonation of the intermediate carbanion. 

---