Regiodivergent Enantioselective γ-Additions of Oxazolones to 2,3-Butadienoates Catalyzed by Phosphines: Synthesis of α,α-Disubstituted α-Amino Acids and N,O-Acetal Derivatives
摘要:
Phosphine-catalyzed regiodivergent enantioselective C-2- and C-4-selective gamma-additions of oxazolones to 2,3-butadienoates have been developed. The C-4-selective gamma-addition of oxazolones occurred in a highly enantioselective manner when 2-aryl-4-alkyloxazol-5-(4H)-ones were employed as pronudeophiles. With the employment of 2-alkyl-4-aryloxazol-5-(4H)-ones as the donor, C-2-selective gamma-addition of oxazolones took place in a highly enantioselective manner. The C-4-selective adducts provided rapid access to optically enriched alpha,alpha-disubstituted alpha-amino acid derivatives, and the C-2-selective products led to facile synthesis of chiral N,O-acetals and gamma-lactols. Theoretical studies via DFT calculations suggested that the origin of the observed regioselectivity was due to the distortion energy that resulted from the interaction between the nudeophilic oxazolide and the electrophilic phosphonium intermediate.
Regiodivergent Enantioselective γ-Additions of Oxazolones to 2,3-Butadienoates Catalyzed by Phosphines: Synthesis of α,α-Disubstituted α-Amino Acids and N,O-Acetal Derivatives
摘要:
Phosphine-catalyzed regiodivergent enantioselective C-2- and C-4-selective gamma-additions of oxazolones to 2,3-butadienoates have been developed. The C-4-selective gamma-addition of oxazolones occurred in a highly enantioselective manner when 2-aryl-4-alkyloxazol-5-(4H)-ones were employed as pronudeophiles. With the employment of 2-alkyl-4-aryloxazol-5-(4H)-ones as the donor, C-2-selective gamma-addition of oxazolones took place in a highly enantioselective manner. The C-4-selective adducts provided rapid access to optically enriched alpha,alpha-disubstituted alpha-amino acid derivatives, and the C-2-selective products led to facile synthesis of chiral N,O-acetals and gamma-lactols. Theoretical studies via DFT calculations suggested that the origin of the observed regioselectivity was due to the distortion energy that resulted from the interaction between the nudeophilic oxazolide and the electrophilic phosphonium intermediate.
Probing the Efficiency of N-Heterocyclic Carbene Promoted <i>O</i>- to C-Carboxyl Transfer of Oxazolyl Carbonates
作者:Jennifer E. Thomson、Craig D. Campbell、Carmen Concellón、Nicolas Duguet、Kathryn Rix、Alexandra M. Z. Slawin、Andrew D. Smith
DOI:10.1021/jo702720a
日期:2008.4.1
Screening of a range of azolium salts, bases and solvents for reactivity indicates that triazolinylidenes, generated in situ with KHMDS in THF, promote the Steglich rearrangement of oxazolyl carbonates with high catalytic efficiency (typical reaction time 5 min at < 1.5 mol % NHC). This protocol shows wide substrate applicability, even allowing the efficient generation of vicinal quaternary centers. An improved experimental procedure is also described that allows a simplified one-pot reaction protocol to be employed with similarly high catalytic efficiency.
Regiodivergent Enantioselective γ-Additions of Oxazolones to 2,3-Butadienoates Catalyzed by Phosphines: Synthesis of α,α-Disubstituted α-Amino Acids and <i>N</i>,<i>O</i>-Acetal Derivatives
作者:Tianli Wang、Zhaoyuan Yu、Ding Long Hoon、Claire Yan Phee、Yu Lan、Yixin Lu
DOI:10.1021/jacs.5b10524
日期:2016.1.13
Phosphine-catalyzed regiodivergent enantioselective C-2- and C-4-selective gamma-additions of oxazolones to 2,3-butadienoates have been developed. The C-4-selective gamma-addition of oxazolones occurred in a highly enantioselective manner when 2-aryl-4-alkyloxazol-5-(4H)-ones were employed as pronudeophiles. With the employment of 2-alkyl-4-aryloxazol-5-(4H)-ones as the donor, C-2-selective gamma-addition of oxazolones took place in a highly enantioselective manner. The C-4-selective adducts provided rapid access to optically enriched alpha,alpha-disubstituted alpha-amino acid derivatives, and the C-2-selective products led to facile synthesis of chiral N,O-acetals and gamma-lactols. Theoretical studies via DFT calculations suggested that the origin of the observed regioselectivity was due to the distortion energy that resulted from the interaction between the nudeophilic oxazolide and the electrophilic phosphonium intermediate.