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Synthesis of a fully functionalised tetracyclic gibberellin intermediate

✍ Scribed by H.J.E. Loewenthal; S. Schatzmiller

Publisher: Elsevier Science
Year: 1972
Tongue: French
Weight: 125 KB
Volume: 13
Category: Article
ISSN: 0040-4039
DOI: 10.1016/s0040-4039(01)93979-6

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✦ Synopsis

In our previous studies on gibberellin synthesis we have described a general approach to the construction of the ring A lactone system as present in gibberellins such as Gibberellic acid and Gibberellin A4 (l), based on the reductive alkylation of a P-methoxybenzoic acid 192 . We have also described an approach to the bicyclo[3,2,1] octane system present in rings C,D of 3,495 these compounds . With a view to combining these two approaches and, in addition, to illustrate a simple method of functionalisation in ring B we now describe the synthesis of a tetracyclic intermediate (5, R=C02Me, R'= -OCH2CH20-) which contains all the functional groups necessary for elaboration to Gibberellin A4. 7-Methoxyindan-l-one 6 was formylated, and the a-formyl ketone treated with hydrogen peroxide in refluxing t-butanol to give the dicarboxylic acid (2, R=R'=H). double m.p. gB", 110". Its half-ester (2_, R=Me, R'=H) was treated with oxalyl chloride and then with aluminium chloride in 1,2-dichloromethane, to give after remethylation (Me2S04/NaOH/THF) the keto-ester (3, R=H), m.p. IlOO. Acid-catalysed condensation of this with n-butyl glyoxalate, followed by catalytic hydrogenation and methanolysis led to the diester (3, R= CH2C02Me), m.p. gB-gg', in 76% overall yield. Treatment of the latter with methyl vinyl ketone in methanolic sodium

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