Catalytic asymmetric dialkynylation reaction of α-dinitrone by utilizing tartaric acid ester as a chiral auxiliary

The asymmetric addition of alkynylzinc reagents, prepared in situ from dimethylzinc and 1-alkynes, to α-dinitrones derived from glyoxal and N-(4-isopropylbenzyl)hydroxylamine was investigated by utilizing dicyclohexyl (R,R)-tartrate as a chiral auxiliary. The addition reaction of methyl(2-phenylethynyl)zinc afforded the corresponding optically active C2-symmetric (R,R)-bis(hydroxylamine) derivative with enantioselectivities of 90% and 81% ee by utilizing a stoichiometric and catalytic amount of the tartrate, respectively. Furthermore, the catalytic addition reaction of several alkynylzinc reagents also furnished the corresponding bis(hydroxylamine) with moderate to good enantioselectivities.

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N,N′-[(R,R)-1,6-Diphenylhexa-1,5-diyne-3,4-diyl]bis[N-(4-isopropylbenzyl)hydroxylamine]C38H40N2O2Ee = 81%[α]D25=+14 (c 0.824, EtOH)Source of chirality: dicyclohexyl (R,R)-tartrateAbsolute configuration: (R,R)

N,N′-[(R,R)-1,6-Diphenylhexa-1,5-diyne-3,4-diyl]bis[N-(benzyl)hydroxylamine]C32H28N2O2Ee = 24%[α]D25=+7 (c 0.73, EtOH)Source of chirality: dicyclohexyl (R,R)-tartrateAbsolute configuration: (R,R)

N,N′-[(R,R)-1,6-Diphenylhexa-1,5-diyne-3,4-diyl]bis[N-(4-chlorobenzyl)hydroxylamine]C32H26N2O2Cl2Ee = 11%[α]D25=+5 (c 0.488, EtOH)Source of chirality: dicyclohexyl (R,R)-tartrateAbsolute configuration: (R,R)

N,N′-[(R,R)-1,6-Diphenylhexa-1,5-diyne-3,4-diyl]bis[N-(3,5-dimethylbenzyl)hydroxylamine]C36H36N2O2Ee = 47%[α]D25=+10 (c 0.584, EtOH)Source of chirality: dicyclohexyl (R,R)-tartrateAbsolute configuration: (R,R)

N,N′-[(R,R)-1,6-Diphenylhexa-1,5-diyne-3,4-diyl]bis[N-(4-t-butylbenzyl)hydroxylamine]C40H44N2O2Ee = 37%[α]D25=+5 (c 0.884, EtOH)Source of chirality: dicyclohexyl (R,R)-tartrateAbsolute configuration: (R,R)

N,N′-[(R,R)-1,6-Bis(4-pentylphenyl)hexa-1,5-diyne-3,4-diyl]bis[N-(4-isopropylbenzyl)hydroxylamine]C48H60N2O2Ee = 76%[α]D25=+13 (c 0.892, EtOH)Source of chirality: dicyclohexyl (R,R)-tartrateAbsolute configuration: (R,R)

N,N′-[(R,R)-1,6-Bis(4-methoxyphenyl)hexa-1,5-diyne-3,4-diyl]bis[N-(4-isopropylbenzyl)hydroxylamine]C40H44N2O4Ee = 72%[α]D25=+12 (c 0.788, EtOH)Source of chirality: dicyclohexyl (R,R)-tartrateAbsolute configuration: (R,R)

N,N′-{(R,R)-1,6-Bis[4-(trifluoromethyl)phenyl]hexa-1,5-diyne-3,4-diyl}bis[N-(4-isopropylbenzyl)hydroxylamine]C40H38N2O2F6Ee = 59%[α]D25=+9 (c 0.912, EtOH)Source of chirality: dicyclohexyl (R,R)-tartrateAbsolute configuration: (R,R)

N,N′-[(R,R)-1,6-Bis(2-fluorophenyl)hexa-1,5-diyne-3,4-diyl]bis[N-(4-isopropylbenzyl)hydroxylamine]C38H38N2O2F2Ee = 74%[α]D25=+11 (c 0.948, EtOH)Source of chirality: dicyclohexyl (R,R)-tartrateAbsolute configuration: (R,R)

N,N′-[(R,R)-Tetradeca-5,9-diyne-7,8-diyl]bis[N-(4-isopropylbenzyl)hydroxylamine]C34H48N2O2Ee = 79%[α]D25=-10 (c 0.248, EtOH)Source of chirality: dicyclohexyl (R,R)-tartrateAbsolute configuration: (R,R)

N,N′-[(R,R)-1,6-Bis(trimethylsilyl)hexa-1,5-diyne-3,4-diyl]bis[N-(4-isopropylbenzyl)hydroxylamine]C32H48N2O2Si2Ee = 70%[α]D25=-9 (c 0.536, EtOH)Source of chirality: dicyclohexyl (R,R)-tartrateAbsolute configuration: (R,R)

N,N′-[(3R,4R)-1,6-Diphenylhexa-1,5-diyne-3,4-diyl] bis{N-(4-isopropylbenzyl)-O-[(1S′,4R′)-4,7,7-trimethyl-2-oxabicyclo[2.2.1]heptane-3-one-1-carbonyl]hydroxylamine}C58H64N2O8Ee = 100%[α]D25=+80 (c 0.14, EtOH)Source of chirality: dicyclohexyl (R,R)-tartrate, (1S,4R)-camphanic chlorideAbsolute configuration: (3R,4R,1S′,4R′)