Lithium diethylcuprate

The construction of the naturally derived narbomycin and tylosin-aglycones by Masamune and coworkers employ identical methodology for seco-acid formation. In each case, Peterson alkenadon of a functionalized aldehyde (not shown) and the silyl ketones (96 R = SiMes Scheme 36) or (99 Scheme 37) efficiently introduced the required ( )-a,3-unsaturation. Silyl ketone formation is accomplished in each case through cuprate acylation by an activated carboxylic acid derivative. Formation of an acid chloride was not possible in the sensitive tylosin-aglycone intermediate however, selective acylation of the silylcuprate proceeded at the pyridyl thiol ester moiety of (98) and not with the r-butyl thiol ester. In a related investigation, (97), an advanced intermediate for 6-deoxyerythronolide B, was obtained from (95) via addition of lithium diethylcuprate to the acid chloride (84% yield). In all the above cases, no addition was observed at the f-butyl thiol ester. 

Due to the inherent C2-symmetry of 37, monotosylation occurs in good yield to provide (25, 35)-l-0-tosyl-2,3-0-isopropylidene-L-threitol (79). Subsequent protection of the the free hydroxyl group, displacement of the tosyl group with lithium diethylcuprate, deprotection. 

What is the major product formed when lithium diethylcuprate reacts with 2-iodopentane in ether at -10°C ... 

Carbon-carbon bond formation between an ethyl anion equivalent and an electrophilic site on the side chain can be accomplished by the reaction between a primary alkyl bromide and lithium diethylcuprate. 

---