Crotylboronates tartrate-derived

Tartrate-derived Chiral Allyl- and Crotylboronate Reagents... 

The tartrate-derived crotylboronate reagents are most useful in the context of double asymmetric reactions with chiral aldehydes [118, 203]. Equations (11.16)-(11.19) demonstrate the utility of ( )-219 and (Z)-213 in the synthesis of dipropionate adducts 105-108. 

A final example of the use of tartrate-derived crotylboronates in natural product synthesis is illustrated in the formal total synthesis of ikarugamicin (Scheme II-11) [179]. Here, Roush and Wada used the asymmetric crotylboration of meso-(t/" -2,4-hexadien-1,6-dial)iron tricarbonyl 266 with (S,S)-(E)-219 to set three stereocenters in their synthesis of the a,s-indacene unit of ikarugamycin. This key reaction provided 267 in 90% yield and >98% ee. Homoallylic alcohol 267 was converted to the allylic acetate 268, which underwent stereoselective ethylation with EtsAl with retention of stereochemistry. The resulting adduct 269 was subsequently elaborated to as -indacene unit 271 through a 15-step synthetic sequence, including the intramolecular Diels-Alder reaction of 270. 

This reaction was first reported by Roush in 1985. It is an enantioselective synthesis of a chiral alcohol by the condensation between a crotylboronate derived from diisopropyl-(/ ,/ )-tartrate and an achiral aldehyde. Therefore, it is known as the Roush crotylboration, ... 

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