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
