Chiral ancillaries in the benzannulations of alkoxy and amino carbene complexes with alkynes

The asymmetric benzannulation of chiral Fischer carbene complexes were inve stigated with a series of complexes bearing either chiral alcohols or chira l amines at the heteroatom stabilizing substituent A set of seven alkenyl c omplexes and one aryl complex were prepared from five chiral alcohols; (1S, 2R,5S)(+)-menthol, (1R,2S)-(-)-trans-2-phenylcyclohexanol, (+/-)-trans-2 me thylcyclopentanol, (+/-)-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 in ductions (0-20% de). The phenyl carbene complex derived from (+)-menthol ga ve good asymmetric induction with 3,3-dimethylbut-1-yne as had been previou sly reported, but the reaction with pent-1-yne gave lower induction and a m uch lower chemical yield. Alkenyl complexes bearing prolinol derivatives as the heteroatom stabilizing substituent also gave very low induction in rea ctions with pent-1-yne and this held true for both E- and Z-isomers of thes e complexes. An alkenyl carbene complex derived from the C-2 symmetrical am ine, 3,5-dimethylmorpholine, reacted with pent-1-yne to give moderate yield s of the (arene)chromium tricarbonyl complex but only in 10% de, High asymm etric inductions were observed for the cyclohexadienone annulation of atrop isomeric 2-(N-methyl-3-methylindolyl) carbene complexes prepared from the c hiral auxiliary, (4R,5S)-5-phenyl-4-methylimidazolidinone. Each atropisomer gives a single and different diastereomer of the same 4H-carbazol-4-one wh ere it is the chiral axis of each atropisomer that controls the sense of in duction and not the chirality of the auxiliary. Thus it is likely that thes e complexes, unlike all of the others examined in this work react with acet ylenes in a process in which the chiral auxiliary is not free to rotate abo ut the carbene carbon in any of the reaction intermediates lending to produ ct formation.