Dicyano compounds cyclization

With adiponitrile, an open-chain dinitrile, however, such cyclization leading to a seven-membered cyclic imine occurs to a much lesser extent (see, e.g., eq. 7.25). The hydrogenative cyclizations have been utilized for the synthesis of pyrrolidine and piperidine derivatives from 1,2- and 1,3-dicyano compounds.118,119... 

The methyl hydrogens in 1,3,5- and 1,4,5-trimethyl tetrazoliums, as well as the proton on C-5 in 2,3-disubstituted tetrazoliums are acidic, and can be abstracted with butyl lithium.289,290 Tetrazolium methylides, e.g., the dicyano derivative (143), and the phenacyl compound (171, R = Ph, R = Me) are known.291 The latter undergoes an unexpected thermal cyclization reaction to yield imidazolones (173) (Scheme 27).292... 

Dicyano-l,3-dimethyluracil (156) undergoes substitution reactions with amines or sodium methoxide to yield 157 (R = NHR or OCH3). Compounds 157 reacted with hydrazines to yield the hydrazino derivative 158, which readily cyclized to the pyrazolo[3,4-[Pg.343]

AT-Formylnor-reticuline, on treatment with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone in methanol, is oxidized to the 4-methoxy-compound (35), which can be cyclized to N-norbisnorargemonine (36) (converted by N- and O-methylation into argemonine) by mineral acid or to the isopavine N-formyl-northalidine (37) by treatment with methanesulphonic acid in acetonitrile. The N-formyl compounds can be reduced to AT-methyl by borane or converted into the secondary bases by hydrazinolysis.69... 

Reaction of the arylamine 62 with the complex salt 52 in acetonitrile at room temperature afforded complex 64 in 87% yield (Scheme 17) [125]. Subsequent oxidative cyclization, aromatization and demetalation using iodine in pyridine provided carbazole 65 in 71% yield. Heating of compound 65 in chlorobenzene in the presence of the acidic cation exchange resin amberlyst 15 led to ring closure with formation of the furo[3,2-a]carbazole 66. Oxidation of the methyl group at C-3 to a formyl group using 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ)... 

This cyclization can be promoted by K3[Fe(CN)6]/NaOH, by hypervalent iodine compounds like the Dess-Martin periodinane [363] or by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) [364] as oxidants. As a common mechanistic feature, the oxidant attacks at the thioiminol 11 (tautomeric with 9) to produce the radical 12, which undergoes 1,5-radical cyclization followed by oxidative aromatization of the radical intermediate 13 to the benzothiazoles (10). 

The concept of their homologation method is outlined in Scheme 11.34. Starting from the 3,4,5,6-tetraalkylphthalates 6, reduction and bromination of two ester groups, alkynylation of the resulting dibromides 87, zirconium-mediated cyclization of diynes 88 with dimethyl acetylenedicarboxylate and subsequent aromatization by DDQ (2,3-dichloro-5,6-dicyano-l,4-benzoquinone) afforded the anthracene derivatives 91 in six steps. Tricyclic compounds 91 thus formed are also substituted phtha-late derivatives, which are the same as 86. The tricyclic skeleton of 91 can again be extended to pentacyclic compounds 92 by the same combination of procedures as for 86 [35],... 

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