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Synthesis 2001; 2001(2): 0200-0220
DOI: 10.1055/s-2001-10796
short paper
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Chiral Ancillaries in the Benzannulations of Alkoxy and Amino Carbene Complexes with Alkynes

Richard P. Hsung* , William D. Wulff, Steven Chamberlin, Ying Liu, Rui-Yang Liu, Huan Wang, John F. Quinn, Siu Ling B. Wang, Arnold L. Rheingold
  • *Searle Chemistry Laboratory, Department of Chemistry, University of Chicago, Chicago, Illinois 60637, USA; Fax +1(517)3531793; E-mail: wulff§rainbow.uchicago.edu
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Publication Date:
31 December 2001 (online)

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The asymmetric benzannulation of chiral Fischer carbene complexes were investigated with a series of complexes bearing either chiral alcohols or chiral amines at the heteroatom stabilizing substituent. A set of seven alkenyl complexes and one aryl complex were prepared from five chiral alcohols; (1S,2R,5S)-(+)-menthol, (1R,2S)-(-)-trans-2-phenylcyclohexanol, (±)-trans-2-methylcyclopentanol, (±)-isoborneol, and (-)-8-phenylmenthol. The reaction of all seven of the alkenyl complexes with pent-1-yne and 3,3-dimethylbut-1-yne gave (arene)chromium tricarbonyl complexes with very low asymmetric inductions (0-20% de). The phenyl carbene complex derived from (+)-menthol gave good asymmetric induction with 3,3-dimethylbut-1-yne as had been previously reported, but the reaction with pent-1-yne gave lower induction and a much lower chemical yield. Alkenyl complexes bearing prolinol derivatives as the heteroatom stabilizing substituent also gave very low induction in reactions with pent-1-yne and this held true for both E- and Z-isomers of these complexes. An alkenyl carbene complex derived from the C-2 symmetrical amine, 3,5-dimethylmorpholine, reacted with pent-1-yne to give moderate yields of the (arene)chromium tricarbonyl complex but only in 10% de. High asymmetric inductions were observed for the cyclohexadienone annulation of atropisomeric 2-(N-methyl-3-methylindolyl) carbene complexes prepared from the chiral auxiliary, (4R,5S)-5-phenyl-4-methylimidazolidinone. Each atropisomer gives a single and different diastereomer of the same 4H-carbazol-4-one where it is the chiral axis of each atropisomer that controls the sense of induction and not the chirality of the auxiliary. Thus it is likely that these complexes, unlike all of the others examined in this work, react with acetylenes in a process in which the chiral auxiliary is not free to rotate about the carbene carbon in any of the reaction intermediates leading to product formation.

asymmetric benzannulation - chiral amine - chiral alcohol - chiral carbene complex - (arene)chromium tricarbonyl - planar chirality - arene complexes