Organolanthanide-catalyzed intra- and intermolecular tandem C-N and C-C bond-forming processes of aminodialkenes, aminodialkynes, aminoalkeneynes, and aminoalkynes. New regiospecific approaches to pyrrolizidine, indolizidine, pyrrole, and pyrazine skeletons

This contribution describes catalytic tandem C-N and C-C bond-forming reactions involving the intramolecular hydroamination/bicyclization and intermolecular hydroamination/cyclization of olefins and alkynes using the organolanthanide complexes Cp'(2)LnCH(SiMe(3))(2) and Me(2)SiCp "(2)LnCH(SiMe(3))(2) (Cp' = eta(5)- Me(5)C(5); Cp " = eta(5)-Me(4)C(5); Ln = lanthanide) as precatalysts. In the case of the intramolecular processes, substrates of the structures RC=C(CH(2))(a)NH(CH(2))(b)C=CR, RC=C(CH(2))(c)NH(CH(2))(d)CH=CH(2), and H(2)C=CH-(CH(2))(e)NH(CH(2))(f)CH=CH(2) are regiospecifically bicyclized to the corresponding pyrrolizidine and indolizidine skeletons, with turnover frequencies ranging from 2 to 777 h(-1) at 21 degrees C and isolated product yields ranging from 85 to 93%. In the case of e = 3 and f = 1 mediated by Cp'(2)Sm-, the kinetic rate lawis zero-order in substrate concentration and first-order in lanthanide concentration. In the case of R = Ph, c = 3, and d = 1, the Cp'(2)Ln-catalyzed turnover frequencies fall precipitously with decreasing Ln(+3) ionic radius. In the intermolecular processes, substrates of the type HC=CCH(2)NHR undergo regiospecific coupling and cyclization to the corresponding pyrroles MeCC(H)=C(<(CH)over bar>(2)NHR)N(R)CH with high turnover frequencies where R and N(t) (h(-1)) are the following: CH(2)=CHCH(2), 236 (60 degrees C); CH(3)CH(2)CH(2), 208 (60 degrees C); CH(2)=CHCH(2)CH(2)CH(2), 58 (60 degrees C). In addition, hydroamination/cyclization processes after intermolecular insertion can be effected when R = CH(2)=CHCH(2), to afford a 2,7-dimethyldipyrrolo[1,2-a:1',2'-d]pyrazine derivative via two successive intramolecular olefin insertion processes. The mechanism for such tandem C-N and C-C bond formations is postulated to involve turnover-limiting intra-or intermolecular alkene/alkyne insertion into the Ln-N functionality, followed by rapid intramolecular insertion of a pendant C=C/C=C-containing functionality into the resulting Ln-C bond (prior to protonolysis). Such a scenario is consistent with well-documented, stepwise transformations in organo-f-element-catalyzed insertions of unsaturated carbon-carbon multiple bonds into metal-amide and metal-alkyl functionalities.