Journal of the American Chemical Society, Vol.121, No.39, 9143-9154, 1999
Utility of a diene-tricarbonyliron complex as a mobile chiral auxiliary: Regio- and stereocontrolled functionalization of acyclic diene ligands
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(lf) 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 2-5 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 3-5 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-ii 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.