Semireduction of alkynoic acids via a transition metal-free α borylation-protodeborylation sequence
作者:Astha Verma、R. Justin Grams、Brett P. Rastatter、Webster L. Santos
DOI:10.1016/j.tet.2019.02.030
日期:2019.4
A method for the semi-reduction of alkynoicacids through an α-borylation and subsequent protodeborylation mechanism has been developed. The transition metal-free protocol is achieved through the activation of bis(pinacolato)diboron by an in situ generated carboxylate moiety yielding aryl acrylic acids. Our studies demonstrate an unprecedented dual role for the carboxylate anion that involves the activation
Substrate‐Assisted, Transition‐Metal‐Free Diboration of Alkynamides with Mixed Diboron: Regio‐ and Stereoselective Access to
<i>trans</i>
‐1,2‐Vinyldiboronates
作者:Astha Verma、Russell F. Snead、Yumin Dai、Carla Slebodnick、Yinuo Yang、Haizhu Yu、Fu Yao、Webster L. Santos
DOI:10.1002/anie.201700946
日期:2017.4.24
A substrate‐assisteddiboration of alkynamides using the unsymmetrical pinacolato‐1,8‐diaminonaphthalenato diboron (pinBBdan) is described. The transition‐metal‐free reaction proceeds in a regio‐ and stereoselective fashion to exclusively afford trans‐vinyldiboronates in good to excellent yields. Notably, Bdan and Bpin are installed on the α‐ and β‐carbon atoms, respectively.
Rhodium(III)-Catalyzed Regioselective Decarboxylative Cyclization for the Synthesis of 4<i>H</i>-Furo[3,2-<i>c</i>]chromen-4-one Derivatives
作者:Dandan Zha、Hongji Li、Shiqing Li、Lei Wang
DOI:10.1002/adsc.201600974
日期:2017.2.2
This contribution describes a regioselective cyclization of hypervalent iodine reagents (HIR) with propiolic acids in the presence of a rhodium catalyst. The mild decarboxylation can tolerate a wide range of groups and generates 4H‐furo[3,2‐c]chromen‐4‐one derivatives in good isolated yields.
该贡献描述了在铑催化剂存在下用丙酸对高价碘试剂(HIR)的区域选择性环化。轻度的脱羧可以耐受广泛的基团,并以良好的分离产率生成4 H-呋喃[3,2 - c ] chromen-4-one衍生物。
Carboxylation of Terminal Alkynes with Carbon Dioxide Catalyzed by an In Situ Ag<sub>2</sub>O/N-Heterocyclic Carbene Precursor System
A carboxylation of terminal alkynes with carbondioxide (CO2) at ambient conditions was developed in situ using a series of N‐heterocyclic carbene (NHC) precursors and Ag2O. The unique structure of NHCs largely increases the solubility of active Ag species and meanwhile activates CO2 by forming the NHC–CO2 adduct. This novel catalytic system demonstrated quite low Ag loading, very high activities,
functionalized dichlorinated vinyl sulfones. This method features excellent regio- and stereoselectivities, good functional group compatibility, as well as mild reaction conditions. Mechanistic studies suggest that the reaction goes through sequential syn-chloropalladation, alkene insertion, and C(sp3)–Cl bond formation processes, and the sulfonyl group is crucial to the stereoselectivity control of the reaction