When reacting with I,. 2-(cyclopt:ni-2-enyl)anilines undergo cyclization into 3-iodot,2.3,3a,4,gb-hexahydrocyclopenlaibtindotes in high yields. The minor reaction products were 3.5-or 3.7-cliiodoindolines. Ammonolysis of 3-iodo-5-methyl-l.2,3.3a,4.Sb-hexahydrocyclopentalhlindcJle or its. :V-cllloroaccly} derivative results in 3-alnino-5-rtleihyl.-t,2.3,3a,4.Sbhcxahydro-arid 5-methyl-1.3a.4.Sb-ietrahydrocyclopel~talblindoles. iodocyclizaiion,2,3,3a,4.gbhcxahydmcyclopenlalblindoles, elinunation,3a.4,3,3a.4,indolc fragments are very' common in nature, in particular, as components of some alkaloids. L! In cyclopentalblindoles obtained from cyclopentanone phenythydrazones 3 by acid-catalyzed "l or photochemical s.f> inlranlofr cyclization of 2-cyc[openlenylanilines, the cyclopcntane fragment is not functionalizcd, thus limiting their use in flinher transform:mons. By contrast, the reaction of 2-(cyclopent-2-enyl/anilines with iodine can not only afford conlpounds of this series, but also provide conditions for their subseqt.eni functionalization. Although halocyclization 7 is widely used in the preparation of various heterocycles, this reaction has been studied only for "l limited set of 2-alkenylanilines. it
Key words:In tile present w'ork, we investigated tile iodocyclization of 2-(cyclopent-2-enyl)anilmes 9 and some transformations of the reaction products. The starting anilines can easily be prepared from comlnercial dicyclopentadiene.
Results and DiscussionThe reaction of arylamine I with I~ in nonpolar solvents (CCI4. C~,He,, or C(,HI2) results in 3-iodo-5-methyl-1.2.3,3a,4,Sb-hexahydrocyclopentalb]indole (2) in 85% yield. The yield of 3,7-diiodo-5-methyl-1,2,3.3a,4.8b-hexahydrocyciopentalb]indole (3) is low (<1%). In polar solvents such as MeCN or EtOH, the reaction is more sluggish. Furthermore, full conversion of amine I into indolme 2 was achieved only upon addition of a new portion of I,. Tile content of diiodide 3 in tile reaction mixture was 6--7%. "Faking into accotlnl the absence of stereo-and regioisomers of indoline 2, we assume that electrophilic addition of iodine to tile double bond of the alkenyl fragment results, via complex 4, in intermediate 5 with subsequent intralnolecul:lr nucleophilic attack of the N atom on C(2",l and 5-exo-cyclization t~ (Scheme I).Analogously, monoiodo derivatives 8 and 9 were the major products (in 86 and 88% yield, respectively} in the reactions of amines 6 and 7 with I-,.However, unlike the cyclization ofarylamine 1 (where only one possible diiodide 3 is Ibrmed), the reactions of 6-(6) and 2-(cyctopent-2-enyl)-3-lnethylaniline (7) with I~ in CCI,a afford two isomeric diiodides, namely, 3"~7-diiodo-6-methyl-(10) or 3,7-diiodo-8-mcthyl-1,2,3,3a,4,Sb-hexahydrocyclopenta[blindoles (1 ! ) and 3,5-diiodo-6-methyl-(12) or 3,5-diiodo-8-methyi-1,2,3,3a,4,Sb-hcx:lhydrocyclopentalblindoles (13), which represent para-and ortho-iodination products with respect to the --N H group, respectively, m 0.3-1% yields.Indoline 2 reacted with chloroacetyl chloride to give compound 14. When...
