Lateral substituents carbonyl groups

The carbonyl group in 24 could be temporarily protected as the dioxolane,16 or somewhat more efficiently as the dimethyl acetal 25.17 Subsequent conventional hydroboration led stereoselectively to the P alcohol 26. Although our earliest considerations called for ultimate base-promoted elimination of the OR substituent in intermediates more advanced than 16, we later came to recognize that a methoxy derivative was not going to fulfill this role to our satisfaction. Alternatively, the tactic of forming the benzyl ether at this point ultimately proved well suited to the eventual return to an unmasked hydroxyl at this site.17,18... 

In preparation for a Robinson annelation, it is often advantageous to increase the reactivity of the position adjacent to the carbonyl group by introduction of a substituent that can later be removed. Thus Turner et al." found direct condensation of 7-methoxy-l-tetralone (1) with methyl vinyl ketone or the corresponding Mannich base to show little promise. They then converted (1) into the 2-hydroxymethylene... 

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