Biomimetic polyene cyclisations

A spectacular application of chiral acetals is in the biomimetic polyene cyclisation to give the steroid skeleton (106) made famous by Johnson. jjere no fewer than seven new stereogenic centres are created in one step. 

A novel sodium ion templated polyene cyclisation reaction has been proposed for the biosynthesis of tetronasin, based on biomimetic studies [91]. This... 

A more serious example is from Johnson s biomimetic polyolefin cyclisation. He wished to make the polyene 111 for potential cyclisation to 110, a 5-6-6-5 ring system analogous to the natural steroids. After the obvious aldol disconnection, it is best to disconnect the /ran.v-alkene 112 in the middle of the molecule. 

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