Synthesis of a C(1)-C(14)-containing fragment of callipeltoside A

(equation presented) A C(1)-C(14)-containing fragment of callipeltoside A (1, Scheme 1) was synthesized efficiently via a dianion aldol coupling reaction between aldehyde 2 and ketoester 3. A surprising lack of reactivity between the alkenes in 13 and the Grubbs initiator 15 was encountered. An equally surprising rate acceleration of the reaction between 15 and allylic alcohols (alk-1-en-3-ols) as well as their subsequent cleavage to methyl ketones was discovered. In situ ¹H NMR analysis has proven to be a very useful tool for monitoring RCM reactions of complex substrates such as 13.