A Highly Stereoselective Synthesis of α-Carbethoxy-α,β-unsaturated Phosphonates Mediated by Tri-n-Butylarsine
摘要:
A highly stereoselective synthesis of alpha-carbethoxy-alpha,beta-unsaturated phosphonates in 71-92% yield mediated by tri-n-butylarsine under neutral condition is described.
A Catalytic Michael/Horner-Wadsworth-Emmons Cascade Reaction for Enantioselective Synthesis of Thiochromenes
作者:Abhijnan Ray Choudhury、Santanu Mukherjee
DOI:10.1002/adsc.201300281
日期:2013.7.8
A catalyticenantioselective sulfa‐Michael/Horner–Wadsworth–Emmonsreactioncascade has been developed, taking advantage of phosphonate as an electrophilic activator and a traceless binding site. Using a chiral bifunctional urea derivative as the catalyst, a variety of aryl and heteroaryl substituted thiochromenes was obtained in excellent yield with a high level of enantioselectivity.
In the presence of titanium tetrachloride and an organic base in tetrahydrofurane, triethyl phosphonoacetic acid undergoes condensation with aliphatic and aromatic aldehydes and aromatic ketones to yield the corresponding triethyl alkylidene and arylidene phosphonoacetic acids respectively. Tetraalkyl methylenediphosphonates and aromatic or aliphatic α-branched aldehydes react under identical conditions
malononitrile to vinyl phosphonates was accomplished by hydrogen bond-enhanced bifunctional halogen bond (XB) catalysis. NMR titration experiments were used to demonstrate that halogen bonding, with the support of hydrogen-bonding, played a key role in the activation of the Michael acceptors through the phosphonate group. This is the first example of the use of XBs for the activation of organophosphorus