A new method has been developed for the catalytic asymmetric synthesis of α-chiral linear or carbocyclic (γ-alkoxyallyl)boronates via the copper(I)-catalyzed γ-boryl substitution of allyl acetals. This reaction afforded the products in high yields with excellent E:Z selectivities and enantioselectivities [only (E)-product, 91-98% ee] and also exhibited high functional group compatibility. Subsequent allylation of aldehydes with the α-chiral (γ-alkoxyallyl)boronates provided the anti-1,2-diol derivatives in a highly stereospecific manner, and the utility of the α-chiral (γ-alkoxyallyl)boronates was further demonstrated by a convergent coupling of a complex polyol derivative using a (γ-alkoxyallyl)boronate and a chiral α-oxyaldehyde. The stereoselective modular construction of a complex 3,3-disubstituted cyclopentene containing three consecutive stereocenters including a quaternary chiral carbon was also reported. Useful transformations of the α-chiral linear (γ-alkoxyallyl)boronates were also demonstrated.
A new C
2-symmetrical P-chirogenic bisphosphine ligand with
silyl substituents on the ligand
backbone, (R,R)-5,8-TMS-QuinoxP*,
has been developed. This ligand showed higher reactivity and enantioselectivity
for the direct enantioconvergent borylation of cyclic allyl electrophiles
than its parent ligand, (R,R)-QuinoxP*
(e.g., for a piperidine-type substrate: 95% ee vs 76% ee). The borylative
kinetic resolution of linear allyl electrophiles was also achieved
using (R,R)-5,8-TMS-QuinoxP* (up
to 90% ee, s = 46.4). An investigation into the role
of the silyl groups on the ligand backbone using X-ray crystallography
and computational studies displayed interlocking structures between
the phosphine and silyl moieties of (R,R)-5,8-TMS-QuinoxP*. The results of DFT calculations revealed that
the entropy effect thermodynamically destabilizes the dormant dimer
species in the catalytic cycle to improve the reactivity. Furthermore,
in the direct enantioconvergent case, detailed calculations indicated
a pronounced enantioselective recognition of carbon–carbon
double bonds, which is virtually unaffected by the chirality at the
allylic position, as a key for the borylation from both enantiomers
of racemic allyl electrophiles.
A novel galvinoxyl-inspired dinitronyl nitroxide (1) has been synthesized. Structural analysis revealed that 1 exhibited a resonance structure resulting from p-benzoquinonediimine N,N'-dioxide and N-phenyl nitroxide moieties. The magnetic study revealed...
A novel approach has been developed for the enantioselective synthesis of α-chiral γ-acetoxyallylboronates via the copper(I)-catalyzed γ-boryl substitution of allyl acylals. This reaction proceeded with high E/Z selectivity and enantioselectivity (E/Z = >99:1, up to 80% yield, up to 99% ee). The subsequent allylation of aldehyde with the allylboronate afforded the monoprotected anti-1,2-diol derivative with high stereoselectivity.
A novel approach for the selective synthesis of α-substituted γ-aminoallylboronates through a copper(I)-catalyzed γ-boryl-substitution of allyl aminals is developed. The reaction proceeds with high yield (up to 88%) and good E/Z selectivity (up to >95:5). Subsequent aldehyde allylation using allylboronates affords (Z)-anti-1,2-amino alcohol derivatives with high stereoselectivity (up to 91% yield, and up to 17:83 E/Z).
Copper(I)-Catalyzed Enantioselective Synthesis of -Chiral Linear or Carbocyclic (E)-(-Alkoxyallyl)boronates.-The title reaction starts from allyl acetates bearing a variety of functional groups and proceeds with high E-selectivity and excellent enantioselectivity. The utility of the method is demonstrated by different transformations of the products: They serve e.g. as substrates for the allylation of functionalized aldehydes, such as alkyl, aryl, alkenyl, and alkynyl aldehydes including chiral aldehyde derivatives, thus providing a stereospecific access to anti-1,2-diols and polyols. The method offers an approach to valuable synthetic intermediates, such as compound (XV) for the preparation of the natural product (-)-massoialactone (XVI). The borylation methodology is applicable to cyclic allyl ketals, such as compound (XVII), allowing the setup of congested stereogenic centers, and enables the construction of complex molecules, such as the cyclopentene derivative (XXIV), with three consecutive stereocenters, including a quaternary one, via iterative borylation/aldehyde allylation sequences. -(YAMAMOTO, E.; TAKENOUCHI, Y.; OZAKI, T.; MIYA, T.; ITO*, H.; J. Am. Chem. Soc. 136 (2014) 47, 16515-16521, http://dx.doi.org/10.1021/ja506284w ; Div. Chem. Process Eng., Fac. Eng.,
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.