Quin uclidine

Only Cram (36) has published a rationale for the very high (99%) enantiomeric excess achieved in the reaction of methyl vinyl ketone and the hydrindanone in the presence of the chiral crown ether. This mechanism envisions a bimolecular complex comprising the potassium cation and chiral host as one entity and the enolate anion of the hydrindanone as the counterion. Methyl vinyl ketone lies outside this complex. The quinine-catalyzed reaction appears to have a termo-lecular character, since the hydroxyl of the alkaloid probably hydrogen bonds with the methyl vinyl ketone—enhancing its acceptor properties—while the quin-uclidine nitrogen functions as the base forming the hydrindanone—alkaloid ion pair. 

The structure of guettardine (72), isolated from Guettarda heterosepala, suggests that this alkaloid may represent an intermediate between the Corynanthe and cinchonamine types of alkaloids (Herbert, 1986). If so, cleavage of the p-carboline system must precede the formation of the quin-uclidine ring (Fig. 34.20) (Herbert, 1986). 

A striking demonstration of the effect of steric hindrance on donor strength is provided by the contrast between Me3B adducts of triethylamine and quin-uclidine. These amines should have essentially the same basicities through inductive effects, but the alkyl groups are pinned back away from the nitrogen in the latter, so that they do not interfere sterically with the trimethylborane. Whereas the adduct with Et3N is hardly formed at all in the vapour phase at... 

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