Tetrahydroindole complexes

C. Diels-Alder Reactions and the Synthesis of Indoles Synthesis of Tetrahydroindole Complexes... 

The uncoordinated portion of the 3-vinylpyrrole complexes described above resembles an electron-rich diene, and undergoes a Diels-Alder reaction under mild conditions with electron-deficient alkenes and al-kynes to give functionalized 5,6,7,7a-tetrahydroindole complexes 122 and 149-164 in moderate to excellent yields (Table 10). In most cases, only one stereoisomer is observed even though up to four new stereocenters are formed. For tetrahydroindole complexes 122 and 150, relative stereochemistry has been assigned and is consistent with cycloaddition occurring through an endo-transition state as well as dienophile attack occurring anti to metal coordination. Furthermore, no isomerization occurs to the 4,5,6,7-tetrahydroindole system, which predominates for uncoordinated tetrahydroindoles.23... 

The conversion of tetrahydroindole complexes to indoles is achieved in moderate to good yields by heating in the presence of 2 equiv of DDQ in either acetonitrile or DMAc solution, the latter of which gives slightly higher yields (Table 11). In this reaction, the oxidant serves both to... 

Demetalation of 4 with trimethylamine N-oxide yields car-bazole 5. Methylation gives carbazomycin A (1) [12]. In addition to carbazoles, Kndiker and his students applied this iron-mediated chemistry to the preparation of dihydroindoles [13, 14], (anhydrolycotine), tetrahydroindoles [15], dihydrocarbazoles [16], perhydroacenaphihenes [17], and azaspiroannelated ring systans [18-21], Several shorter accounts of Kndlker s carbazole syntheses [22-25] and the overall utility of tricarbonyl(Tl -diene)iron complexes in organic synthesis are available [26-32],... 

SCHEME 2.131 Reaction of N-vinyl-4,5,6,7-tetrahydroindole with DMF/POCI3 complex. 

Scheme 4-126. Tetrahydroindoles by oxidative cyclization of amine tethered (Ti -diene)iron complexes.

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