- Enantioselective [3 + 2] annulation of 4-isothiocyanato pyrazolones and alkynyl ketones under organocatalysis
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An asymmetric [3 + 2] annulation reaction of 4-isothiocyanato pyrazolones with alkynyl ketones in the presence of an organic catalyst derived from a cinchona alkaloid under mild conditions is realized. This protocol provides unprecedented expeditious access to a wide range of optically active spiro[pyrroline-pyrazolones] with various electronic properties in high yields with good to excellent enantioselectivities.
- Wang, Wenyao,Wei, Shiqiang,Bao, Xiaoze,Nawaz, Shah,Qu, Jingping,Wang, Baomin
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p. 1145 - 1154
(2021/02/16)
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- C-F bond cleavage enabled redox-neutral [4+1] annulation via C-H bond activation
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Using α,α-difluoromethylene alkyne as a nontraditional one-carbon reaction partner, a synthetically novel method for the construction of isoindolin-1-one derivatives via Rh(III)-catalyzed [4+1] annulation reaction is reported. The 2-fold C-F bond cleavage not only enables the generation of desired product under an overall oxidant-free condition but also results in a net migration of carbon-carbon triple bond. In addition, the present reaction protocol exhibits a tolerance of a wide spectrum of functional groups due to the mild reaction conditions employed.
- Wang, Cheng-Qiang,Ye, Lu,Feng, Chao,Loh, Teck-Peng
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p. 1762 - 1765
(2017/02/15)
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- Catalytic enantioselective construction of β-quaternary carbons via a conjugate addition of cyanide to β,β-disubstituted α,β-unsaturated carbonyl compounds
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The first general catalytic enantioselective conjugate addition of cyanide to β, β-disubstituted α,β-unsaturated ketones and N-acylpyrroles was developed using a strontium catalyst derived from Sr(O iPr)2 and new chiral ligand 5. The reaction exhibited excellent enantioselectivity and a wide substrate scope using 0.5-10 mol % catalyst. 1,4-Adducts containing β-quaternary carbons were exclusively produced over 1,2-adducts. ESI-MS analysis of the strontium catalyst indicated that the active catalyst was a trimetallic Sr/5 = 3:5 complex. The exclusive 1,4-selectivity was partly due to the ability of the strontium complex to promote both a retro-cyanation reaction from the 1,2-adducts and highly enantioselective conjugate cyanation.
- Tanaka, Yuta,Kanai, Motomu,Shibasaki, Masakatsu
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supporting information; experimental part
p. 8862 - 8863
(2010/08/21)
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- Formation of chiral C(sp3)-C(sp) bond by allylic substitution of secondary allylic picolinates and alkynyl copper reagents
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(Chemical Equation Presented) To establish allylic substitution of secondary allylic alcohol derivatives with alkynyl copper reagents, allylic esters bearing the (2-pyridine)CO2-, (2-pyrazine)CO2-, (EtO)2PO2-, C6F5CO2-, o-(Ph2P)-C6H4CO2-, MeOCO 2-, or. AcO- group were examined. First, picolinate (R 1=Me, R2=CH2OPMB) was subjected to reaction with (TMS-C≡C)2CuLi 3 LiBr at 0 °C. Although no substitution took place, MgBr2 (3 equiv) was found to promote the reaction to produce the anti SN2′ product in 93% yield with 94% regioselectivity and 99% chirality transfer. In contrast, substitution of the other esters with the copper reagent in the presence of MgBr2 were less reactive ((2-pyrazine)CO2-) or marginally reactive (other cases). Generality of the substitution using picolinates was established with five picolinates (R1=Me, Ph(CH2)2, PMBO(CH 2)3; R2=Me, CH2OPMB, CH 2OTBS, C5H11, c-C6H11) and seven alkynyl copper reagents (R3=TMS, Ph, p-TBSOC 6H4, p- and o-MeOC6H4, p-MeC 6H4, p-FC6H4), furnishing anti SN2′ products in 61-93% yields with high regioselectivity (usually >90%) and high chirality transfer (usually >95%). In addition, transformation of the products was briefly studied. 2009 American Chemical Society.
- Kiyotsuka, Yohei,Kobayashi, Yuichi
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supporting information; experimental part
p. 7489 - 7495
(2010/01/06)
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