Epiallogibberic acid

The methyl esters of keto acids (XLVI) and (XLVII) from both alio and epiallogibberic acids show positive Cotton effects so that the acetic acid side chain at C-8a must be -oriented. This means that the carboxyl group and ring D must be -oriented in alio- and epiallogibberic acids. 

Alio- and epiallogibberic acids are epimeric at position 4b. This is shown in the following way. 

It follows that epiallogibberic acid has the absolute configuration (XLIII, Figure 10). 

Intramolecular aUol condensation. In a synthesis of a precursor to epiallogibberic acid, House et al. effected an unfavorable intramolecular aldol condensation by use of a covalent magnesium alkoxide intermediate. Thus treatment of (1) with 2eq. of... 

Figure 2.10 Synthesis of epiallogibberic acid. Modified by permission of Shokabo Publishing Co., Ltd...

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