Biomimetic synthesis of steroids

Strategies based on very particular and specific reactions, such as Diels-Alder addition, either inter- or intramolecular (see also cycloeliminations), cationic cyclisations (important in the "biomimetic synthesis" of steroids), Pauson-... 

Allylic alcohol (166) is the product of right-to-left linear iteration by this process. Not only is the tri-substituted alkene accessible with high stereochemical control, but also the ( )-disubstituted alkene is readily prepared. These linear polyenes play an important role in the biomimetic synthesis of steroids and higher terpenes. ... 

On this subject, eventually, Demuth has recently reported the shortest biomimetic synthesis of steroidal skeletons in enantiopure form [40], Using the photoinduced electron transfer (PET) technology, he examined the behavior of diastereomeric )-geranylgeranylmethyl 82 and 86 bearing a (—)-menthone-based chiral auxiliary. Irradiation of 82 provided the two diastereomers 83 and 84 in a 1 7 ratio, and in 10% yield (Scheme 25). The a -trans chair approach from the a-face (82-a+ ) appears much more favorable than that from the j8-face because of steric interactions with the chiral auxiliary. Enantiopure C-17-substituted steroid 85 was... 

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