Regioselective <i>Anti</i>-Silyllithiation of Propargylic Alcohols
作者:Somnath N. Karad、Hayate Saito、Jun Shimokawa、Hideki Yorimitsu
DOI:10.1021/acs.joc.2c01795
日期:——
series of propargylic alkoxides regioselectively in an anti-fashion. Upon treatment with a variety of electrophiles, the trisubstituted alkenyl lithium intermediates were transformed into highly functionalized β-silyl allylic alcohols with high regiocontrol, eventually providing tri- or tetrasubstituted alkenylsilanes stereoselectively. A classic trick for anti-addition with propargylic alkoxides has
作者:Arribas, Andrés、Calvelo, Martín、Rey, Alejandro、Mascareñas, José L.、López, Fernando
DOI:10.1002/anie.202408258
日期:——
An iridium-catalyzed cycloisomerization of N-allenyl pyrroles and indoles is reported. The method, which is initiated by a C−H activation step, delivers a diversity of synthetically relevant azaheterocyclic products, depending on the precise ancillary ligand used and the substitution pattern of the allene. Particularly attractive are the hydrocarbonation cascades of tetrasubstituted allenyl precursors
Alkaline Earth Catalysis of Alkynyl Alcohol Hydroalkoxylation/Cyclization
作者:Christine Brinkmann、Anthony G. M. Barrett、Michael S. Hill、Panayiotis A. Procopiou、Stephanie Reid
DOI:10.1021/om3008663
日期:2012.10.22
Heavier alkaline earth bis(trimethylsilyl)amides [AeN(SiMe3)(2)}(2)](2) (Ae = Ca, Sr, Ba) are shown to act as effective precatalysts for the regioselective intramolecular hydroalkoxylation/cyclization of a wide range of alkynyl and allenyl alcohols. In the majority of cases, cyclization of alkynyl alcohols produces mixtures of the possible endo- and exocyclic enol ether products, rationalized as a consequence of alkynylalkoxide isomerization to the corresponding allene derivatives. Cyclization rates for terminal alkynyl alcohols were found to be significantly higher than for substrates bearing internal alkynyl substituents, while the efficacy of cyclization was in general found to be determined by a combination of stereoelectronic influences and the thermochemical viability of the specific alkaline earth metal catalysis, which we suggest is determined by the individual M-O bond strengths. Kinetic studies have provided a rate law pertaining to a pronounced catalyst inhibition with increasing [substrate], indicating that turnover-limiting insertion of C-C unsaturation into the M-O bond requires the dissociation of substrate molecules away from the Lewis acidic alkaline earth center.
Landor,S.R. et al., Journal of the Chemical Society. Perkin transactions I, 1974, p. 557 - 561
作者:Landor,S.R. et al.
DOI:——
日期:——
Intramolecular Nucleophilic Acyl Substitution Reaction of 3,4-Alkadienyl Carbonates Mediated by Ti(O-<i>i</i>-Pr)<sub>4</sub>/2 <i>i</i>-PrMgCl Reagent. Efficient Synthesis of Optically Active β,γ-Unsaturated Esters with an α-Substituent
作者:Yukio Yoshida、Sentaro Okamoto、Fumie Sato
DOI:10.1021/jo961401t
日期:1996.1.1
readily generated by the reaction of Ti(O-i-Pr)(4) with 2 i-PrMgCl, resulted in an intramolecular nucleophilic acyl substitution (INAS) reaction to afford vinyltitanium compounds 3 which, in turn, reacted with H(3)O(+), D(2)O, or iodine to give alpha-substituted beta,gamma-unsaturated esters 4 in good to excellent yields. The olefin moiety of the hydrolysis product 4 has (Z)-geometry mainly except for