Brown s crotylboration

Brown s crotylboration protocol was used effectively in the synthesis of azu-mamide A 28. Azumamides are unusual cyclic peptides that show potent inhibitory activity on histone deacetylase enzymes. A highly diastereo- and enan-tioselective (dr >99% 98% ee) crotylation of 3-benzyloxypropanal with the chiral reagent ( >crotyl-1Ipc2borane (l19E) afforded the homoallylic alcohol 29. Subsequent reductive ozonolysis and K2CO3-mediated hydrolysis of the acetate furnished the diol 3016 (Scheme 3.1m). 

Synthesis of the chiral Cj-Cio fragment was started from the aldehyde 40 derived from cis-butendiol (Scheme 9). Brown s crotylboration (30) of 40 using (-)-(E)-crotyldiisopinocampheyl-... 

The C29-C34 fragment, trans vinyl iodide 159, is distinguished by two contiguous stereogenic centers, and it was surmised that both could be introduced in a single step through the application of Brown s effective asymmetric crotylboration methodology (see Scheme 48).79 Depro-... 

Brown, H. C. Bhat, K. S. Randad, R. S. Chiral Sjmthesis via Otganoboranes. 21. AUyl- and Crotylboration of Alpha-Chiral Aldehydes with Diisopinocampheylboron as the Chiral Auxiliary.. Org. Chem. 1989, 54, 1570-1576. 

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