20652-39-5Relevant articles and documents
Short Convergent Synthesis of the Mycolactone Core Through Lithiation-Borylation Homologations
Brown, Christopher A.,Aggarwal, Varinder K.
, p. 13900 - 13903 (2015)
Using iterative lithiation-borylation homologations, the mycolactone toxin core has been synthesized in 13 steps and 17 % overall yield. The rapid build-up of molecular complexity, high convergence and high stereoselectivity are noteworthy features of thi
Investigation of the Deprotonative Generation and Borylation of Diamine-Ligated α-Lithiated Carbamates and Benzoates by in Situ IR spectroscopy
Mykura, Rory C.,Veth, Simon,Varela, Ana,Dewis, Lydia,Farndon, Joshua J.,Myers, Eddie L.,Aggarwal, Varinder K.
supporting information, p. 14677 - 14686 (2018/11/20)
Diamine-mediated α-deprotonation of O-alkyl carbamates or benzoates with alkyllithium reagents, trapping of the carbanion with organoboron compounds, and 1,2-metalate rearrangement of the resulting boronate complex are the primary steps by which organoboron compounds can be stereoselectively homologated. Although the final step can be easily monitored by 11B NMR spectroscopy, the first two steps, which are typically carried out at cryogenic temperatures, are less well understood owing to the requirement for specialized analytical techniques. Investigation of these steps by in situ IR spectroscopy has provided invaluable data for optimizing the homologation reactions of organoboron compounds. Although the deprotonation of benzoates in noncoordinating solvents is faster than that in ethereal solvents, the deprotonation of carbamates shows the opposite trend, a difference that has its origin in the propensity of carbamates to form inactive parasitic complexes with the diamine-ligated alkyllithium reagent. Borylation of bulky diamine-ligated lithiated species in toluene is extremely slow, owing to the requirement for initial complexation of the oxygen atoms of the diol ligand on boron with the lithium ion prior to boron-lithium exchange. However, ethereal solvent, or very small amounts of THF, facilitate precomplexation through initial displacement of the bulky diamines coordinated to the lithium ion. Comparison of the carbonyl stretching frequencies of boronates derived from pinacol boronic esters with those derived from trialkylboranes suggests that the displaced lithium ion is residing on the pinacol oxygen atoms and the benzoate/carbamate carbonyl group, respectively, explaining, at least in part, the faster 1,2-metalate rearrangements of boronates derived from the trialkylboranes.
Stereocontrolled synthesis of 1,5-stereogenic centers through three-carbon homologation of boronic esters
Unsworth, Phillip J.,Leonori, Daniele,Aggarwal, Varinder K.
supporting information, p. 9846 - 9850,5 (2014/10/15)
Allylic pinacol boronic esters are stable toward 1,3-borotropic rearrangement. We developed a PdII-mediated isomerization process that gives di- or trisubstituted allylic boronic esters with high E selectivity. The combination of this method with lithiation-borylation enables the synthesis of carbon chains that bear 1,5-stereogenic centers. The utility of this method has been demonstrated in a formal synthesis of (+)-jasplakinolide. Three more: The 3C homologation of chiral pinacol boronic esters gives di- or trisubstituted allylic boronic esters with high yield and E selectivities. The combination of this method with lithiation-borylation enables the synthesis of alkyl chains that bear 1,5-stereogenic centers. The utility of the process was demonstrated in a formal synthesis of (+)-jasplakinolide.
