Ergosterol ozonolysis

Ergosta-5,7,22,24(28)-tetraen-3jS-ol has been synthesised from ergosterol by ozonolysis to the 22-aldehyde and construction of the appropriate side-chain using a Wittig reaction. During these reactions, the 5,7-diene system was protected as the Diels-Alder adduct (546) with 4-phenyl-l,2,4-triazolin-3,5-dione, from which the homoannular diene could be regenerated in 99 % yield by reduction with lithium aluminium hydride. 

By far the most widely used starting material for side chain elaboration schemes has been the C-22 aldehyde. This compound, readily obtained from the ozonolysis of sigmasterol i-ether or the 4-phenyl-l, 2,4-triazoline-3,5-dione (PTAD)-diene adduct of ergosterol has been modified in a number of ways. 

In 1931, it was shown by Reindel and Kipphan that ozonolysis (Oj) of ergosterol acetate in petroleum ether-ethyl acetate produced a mixture containing 2,3-dimeth-ylbutanal, thus identifying the side chain and the position of the double bond therein (Equation 13.3). 

---