Homoallenyl alcohols

The catalytic asymmetric allenylation has been explored with a BINOL/Ti system, giving selectively the homoallenyl alcohol with up to 95% ee. Nevertheless, the lower reactivity of aUenyltin compared to allyltin necessitated a nearly stoichiometric amount of 8. Recently, an improvement of the reaction by using i-PrSBEt2 overcame that limitation, making the system truly catalytic, with ee in the range of 81 to 97% . Interestingly, this reaction showed an unexpected equilibration phenomenon, thus producing exclusively... 

Dienols. Allylindium reagents add to 2,3-butadienols in a manner regulated by chelation. There are certain structural limitations regarding the y-selective attack of the reagents, and thus tertiary carbinols and homoallenyl alcohols, as well as allenyl ethers, fail to react. 

Brown and co-workers developed a novel homoallenyl boronate reagent 169 based on diisopropyl tartrate for the stereoselective homoallenylation of aldehydes 170. The reagent 169 was prepared via homologation of the corresponding allenyl boronate or the alkylation of halomethyl boronate with allenyl Grignard similar to those reported in Scheme 26. The allyl boronate 169 upon reaction with aldehydes furnished the dienyl alcohols 172 with high ee (Scheme 28) <1996JOC100>. 

E.A. Theodorakis and co-workers reported the total synthesis of clerocidin, a diterpenoid antibiotic. To form the C12 stereocenter and the diene moiety, they applied an asymmetric homoallenylboration method. The reaction of the aldehyde and (S,S)-diisopropyltartrate-derived homoallenyl boronate provided the alcohol with a 6 1 diastereoselectivity and 83% yield. 

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