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Utility of a Diene−Tricarbonyliron Complex as a Mobile Chiral Auxiliary:  Regio- and Stereocontrolled Functionalization of Acyclic Diene Ligands

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journal contribution
posted on 21.09.1999, 00:00 by Yoshiji Takemoto, Naoki Yoshikawa, Yasutaka Baba, Chuzo Iwata, Tetsuaki Tanaka, Toshiro Ibuka, Hirofumi Ohishi
Stereoselective construction of contiguous stereogenic centers of acyclic compounds by using the Fe(CO)3 moiety as a mobile chiral auxiliary is described. Although the reactions of acyclic (pentadienyl)iron(1+) cations with nucleophiles generally occur in a stereoselective but nonregioselective manner, giving rise to several regioisomers, O-acyl and O-phosphoryl cyanohydrin Fe(CO)3 complexes 25 undergo regio- and stereoselective 1,5-nucleophilic substitution with several heteroatomic nucleophiles, giving the 6-substituted hepta-2,4-dienonitrile Fe(CO)3 complexes 6 and 7, that is, 1,2-migration products of the Fe(CO)3 group. These products were obtained as single products, even if the starting materials 35 were a mixture of diastereomers. The (2E,4E)/(2E,4Z) selectivity of the 1,5-substituted products (6/7) is strongly dependent on the Lewis acid catalyst, triphenylcarbenium perchlorate (TrClO4) giving 6 (method A) and BF3·etherate giving 7 (method B), respectively. Furthermore, by applying iterative 1,5-nucleophilic substitution to 6, both 6,7-anti-disubstituted (2E,4E)-adduct anti-10 and 6,7-syn-disubstituted (2E,4Z)-one syn-11 were synthesized stereoselectively by switching the reaction conditions (method A and method B). The third introduction of the ethylsulfanyl group into anti-10 proceeded efficiently by the same treatment of 10 with ethanethiol and TrClO4 to afford the 6,7-anti-7,8-anti-trisubstituted (2E,4E)-adduct 19. Further manipulation successfully converted 19 to the N-Boc-O-Me derivative 24 of anti-2,3-amino alcohol 25, which had been isolated from a marine sponge.