Categories: Synthesis of O-Heterocycles > benzo-fused O-Heterocycles >
Synthesis of chromans and flavanes
Recent Literature
A convergent three-step method provides 2-substituted chromans via Heck coupling
of readily accessible allylic alcohols and 2-iodophenols, followed by reduction
and Mitsunobu cyclization. The utility and generality of this method is
demonstrated through the synthesis of a series of 2-aryl-, 2-heteroaryl- and
2-alkylchromans, as well as an azachroman derivative. A Noyori-catalyzed ketone
reduction enables an asymmetric version.
R. K. Orr, L.-C. Campeau, H. R. Chobanian, H. M. McCabe Dunn, B. Pio, C. W.
Plummer, A. Nolting, R. T. Ruck, Synthesis, 2017,
49, 657-666.
A bifunctional aminoboronic acid facilitates intramolecular aza- and
oxa-Michael reactions of α,β-unsaturated carboxylic acids. The combination of an
arylboronic acid with a chiral aminothiourea enables enantioselective
conversions to afford the desired heterocycles in high yields and ee’s (up to
96% ee).
T. Azuma, A. Murata, Y. Kobayashi, T. Inokuma, Y. Takemoto, Org. Lett.,
2014,
16, 4256-4259.
Rh-catalyzed asymmetric transfer hydrogenation enables a straightforward
access to enantiomerically enriched cis-3-benzyl-chromanols from (E)-3-benzylidene-chromanones
in the presence of HCO2H/DABCO as the hydrogen source.
R. M. Betancourt, P. Phansavath, V. Ratovelomanana-Vidal, Org. Lett., 2021, 23,
1621-1625.
Cooperative asymmetric catalysis with hydrogen chloride (HCl) and chiral
dual-hydrogen-bond donors (HBDs) enables a highly enantioselective Prins
cyclization of a wide variety of simple alkenyl aldehydes. The optimal chiral
catalysts withstand the strongly acidic reaction conditions and induce rate
accelerations of 2 orders of magnitude over reactions catalyzed by HCl alone.
D. A. Kutateladze, E. N. Jacobsen, J. Am. Chem. Soc.,
2021, 143, 20077-20083.
A Ru-catalyzed asymmetric transfer hydrogenation of 2,3-disubstituted
flavanones provides chiral flavanols with three contiguous stereocenters with
excellent ees and drs. The reaction proceeds via a base-catalyzed
retro-oxa-Michael addition to racemize two stereogenic centers simultaneously in
concert with a highly enantioselective ketone transfer hydrogenation step.
Q.-X. Xie, L-X. Liu, Z.-H. Zhu, C.-B. Yu, Y.-G. Zhou, J. Org. Chem., 2022, 87,
7521-7530.