Synthesis Golf II: Erythronolide B
I have established the stereochemistry via Evans aldol addition:

Then, after protection of the hydroxyl group, the chiral auxiliary can be transformed to a Weinreb amide which will be attacked by Grignard reagent:

The methyl ketone is then transformed to an alkyne which is methylated:
Finally, hydroboration (should be very regioselective) of the alkyne will provide the trans alkenylborane which on treatment with NaOH and iodine will provide target 12:


Length (total steps and longest linear sequence): 7 steps