When the crude imines 16 and 17 were treated with 10c under conditions previously developed for the pentadienylation of 11, the branched adducts 18 and 19 were formed with high (>10:1) regioselectivity.
These adducts were not purified, but rather they were treated directly with ethylene oxide at 60 C in MeOH in a sealed tube to deliver the corresponding alcohols 20 and 21.
After a single recrystallization, 20 and 21 were isolated in 71% overall yields from 16 and 17, respectively.
Protection of the primary alcohol groups in 20 and 21 as their TBS ethers then afforded 22 and 23.