0277-5387/00/$ - see front matter q2000 Elsevier Science Ltd All rights reserved. PII S0277-5387 ( 99 ) 00404-0 Monday Mar 20 12:05 PM StyleTag -- Journal: POLY (Polyhedron) Article: 3349 www.elsevier.nl/locate/poly Polyhedron 19 (2000) 545–548 Addition of the alkenyl C–H bond of enamines to h 3 -allenyl/propargyl complexes leading to the formation of pyrrole derivatives An-Chi Yeh, Shang-I Chen, Ai-Jan Chen, Gene-Hsiang Lee, Yu Wang, Jwu-Ting Chen * Department of Chemistry, National Taiwan University, Taipei, 106 Taiwan, Republic of China Received 4 October 1999; accepted 24 November 1999 Abstract The reactions of enamines (ROC)HC_CMe(NH i Pr) with h 3 -allenyl/propargyl complexes [M(PPh 3 ) 2 (h 3 -C 3 H 3 )] q (MsPd, Pt) result in the formation of pyrrole derivatives. Such reactions involve the intermediates of central-carbon-substituted h 3 -allyl complexes {M(PPh 3 ) 2 (h 3 -CH 2 C[C(COR)_CMe(NH i Pr)]CH 2 )} q which are formed by hydroalkenylation to the C 3 H 3 moiety. q2000 Elsevier Science Ltd All rights reserved. Keywords: Enamine; Alkenylation; Pyrrole 1. Introduction The addition of an olefinic C–H bond across an unsaturated carbon–carbon bond is highly interesting from the viewpoint of synthetic methodology [1]. The involvement of transition metal complexes in such processes is often crucial, particu- larly for the development of novel ways of C–C bond for- mation [2]. We and other groups have discovered that cationic h 3 -allenyl/propargyl complexes generally behave as good carbon electrophiles and are subject to the addition with a wide variety of nucleophiles containing O, S, Se, N, P or C donor [3–7]. Meanwhile, such complexes exhibit keen chemical selectivity. For instance, tertiary amine such as Et 3 N can be added to [Pt(PPh 3 ) 2 (h 3 -C 3 H 3 )] q (3) via C–N bond formation to give a platinacyclobutene adduct [8]. In con- trast, compound 3 activates a phenyl C–H bond in NMe 2 Ph to allow arylation, yielding an arylallyl complex [9]. We have chosen to use enamines that are known to contain both active N–H as well as C–H bonds to react with h 3 - allenyl/propargyl complexes. Our studies lead to the discov- ery of the first examples of hydroalkenylation of metal complexes of allenyl/propargyl. The insertion of h 3 -C 3 H 3 to an enamine C–H bond affords a diene ‘skeleton’ which allows incorporation of an amino functionality to form the pyrrole derivatives. * Corresponding author. Tel: q886-2-2366-0352; fax: q886-2-2363- 6359; e-mail: jtchen@ccms.ntu.edu.tw 2. Results and discussion The enamines Me(NH i Pr)C_CHR [RsCOMe (1a), CO 2 Me (1b)] have been prepared by the reactions of a,g- diketone or ketoester methane, respectively, with i PrNH 2 [10]. The NMR data for compounds 1a and 1b indicate that tautomerization overwhelmingly inclines to the enamine form, which is presumably stabilized by hydrogen bonding between N–H and the keto group: (1) Previous studies have shown that amines and amino deriv- atives with active hydrogen are prone to undergo regioselec- tive hydroamination to [M(PPh 3 ) 2 (h 3 -C 3 H 3 )] q [MsPd (2), Pt (3)], yielding azatrimethylenemethane (N-TMM) complexes and their derivatives (N-TMM represents the azatrimethylenemethane complexes M[CH 2 C(NR)CH 2 ]) [11]. However, heating a mixture of compounds 2 and 1b at 508C was found to generate the pyrrole derivatives. Further investigation shows that reactions of equimolar amounts of compound 2 and enamine at 258C undergo unprecedented hydroalkenylation. The regioselective C–C coupling takes place between the central carbon of the C 3 H 3 and the b- olefinic carbon of the enamine, and results in enamine– allyl complexes of the formula of Pd(PPh 3 ) 2 {h 3 -CH 2 C-