Stereochemistry torquoselectivity

As with many asymmetric processes, there are three ways to control absolute stereochemistry in the Nazarov cyclization Asymmetry transfer, the use of chiral auxiliaries, or asymmetric catalysis. It is important to realize, however, that there are two distinct processes operating that determine the stereochemistry of the product. To control the absolute stereochemistry of the p-carbon atom(s), it is necessary to control the sense of conrotation, clockwise or counterclockwise (torquoselectivity, see Section 3.4.3). To control the absolute stereochemistry of the a-carbon atom however, it is necessary to control the facial selectivity for enol protonation. 

The relative stereochemistry between the C(3) and C(18) stereocentres of the dodecahydroindolo[2,3-fl]benzo[ ]quinolizine skeleton of reserpine-type alkaloids has been reported from a highly torquoselective thermal triene 6k electrocyclization (Scheme 30)." ... 

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