Monday, July 8, 2013
Tristan H. Lambert
Construction of Alkylated Stereocenters: The Deng Synthesis of (-)-Isoacanthodoral
Matthew S. Sigman at the University of Utah developed (Science 2012, 338, 1455. ) a redox-relay strategy that allowed for the enantioselective Heck arylation of alcohol 1 with diazo salt 2 to produce γ-arylated aldehyde 4 with high ee. Stephen P. Fletcher at the University of Oxford reported (Nature Chem. 2012, 4, 649. ) a procedure that utilized alkenes as alkylmetal equivalents for asymmetric conjugate additions, such as in the conversion of cyclohexenone 5 to ketone 7. A catalytic method for the regioselective and highly enantioselective 1,6-addition of alkynes to α,β,γ,δ-unsaturated carbonyls (e.g. 8 to 9) was reported (J. Am. Chem. Soc. 2012, 134, 18936. ) by Takahiro Nishimura at Kyoto University and Tamio Hayashi at the IMRE in Singapore. Scott E. Schaus at Boston University found (J. Am. Chem. Soc. 2012, 134, 19965. ) that BINOL 12 catalyzed the enantioselective addition of aryl or vinyl boronates to o-quinone methides, such as that generated from 10 to furnish 13.
Elizabeth R. Jarvo at the University of California at Irvine discovered (Angew. Chem. Int. Ed. 2012, 51, 7790. ) that triarylmethanes such as 15 could be prepared by enantiospecific cross-coupling of diarylmethane ethers, as long as the ether was capable of chelation (e.g. 14). Alternatively, Mary P. Watson at the University of Delaware found (J. Am. Chem. Soc. 2013, 135, 3307. ) that benzylic pivalates could be enantiospecifically cross-coupled with arylboroxines, as in the conversion of 16 to 17.
Yoann Coquerel and Jean Rodriguez at the University of Aix-Marseille found (Org. Lett. 2012, 14, 4686. ) that β-ketoamides could be directly arylated by reaction with in situ-generated aryne intermediates, such as in the conversion of 18 to 20. A unique approach to the asymmetric formation of acyclic quaternary stereocenters via a carbometalation-oxidation-aldol cascade of alkyne 21 to produce 22 was reported (Nature 2012, 490, 522. ) by Ilan Marek at the Technion-Israel Institute of Technology. Keiji Maruoka at Kyoto University reported (J. Am. Chem. Soc. 2012, 134, 16068. ) the first organocatalytic conjugate addition of aldehydes to acrylate esters by making use of amine catalyst 25 and the highly electrophilic fluorinated acrylate 23. The stereoselective vinylogous Mukaiyama-Michael reaction of dienol silyl ethers such as 28 with aldehydes by iminium activation with catalyst 29 was reported (Angew. Chem. Int. Ed. 2012, 51, 12609. ) by Christoph Schneider at Leipzig University.
A procedure for the deracemization of α-aryl hydrocoumarins was reported (J. Am. Chem. Soc. 2012, 134, 18245. ) by Benjamin List at the Max Planck Institute in Mülheim, which involved their conversion to ketene dithioacetals (cf. 31 to 32), asymmetric protonative cyclization with chiral phosphonic acid catalyst 33, and finally deprotection to return the hydrocoumarin 35 in enantioenriched form.
Finally, Li Deng at Brandeis reported (J. Am. Chem. Soc. 2012, 134, 18209. ) that cinchona alkaloid-derived 38 catalyzed the enantioselective isomerization of β,γ-unsaturated cyclohexenone 37 to the α,β-unsaturated cyclohexenone 39. Ketone 39 was carried forward in two pots to (-)-isoacanthodoral (40).
T. H. Lambert, Org. Chem. Highlights 2013, July 8.