Enantioselective Alkoxylation of Β-Substituted Aromatic Nitroalkenes with Allyl Alcohol

Allyltrimethylsilane (allyl-TMS) reacts with propargylic alcohols 1a-1d in the presence of 10% Bi(OTf)(3) in [BMIM][BF(4)] solvent to furnish the corresponding 1,5-enynes in respectable isolated yields (87-93%) at room temperature. The utility of Bi(OTf)(3) as a superior catalyst was demonstrated in a survey study on coupling of allyl-TMS with employing several metallic triflates (Bi, Ln, Al, Yb) as well as, B(C(6)F(5))(3), Zn(NTf(2))(2) and Bi(NO(3))(3)·5H(2)O. Coupling of cyclopropyl substituted propargylic alcohol with allyl-TMS gave the skeletally intact 1,5-enyne and a ring opened derivative as a mixture. Coupling of propargylic/allylic alcohol with allyl-TMS resulted in allylation at both benzylic (2 isomers) and propargylic positions, as major and minor products respectively. The scope of this methodology for allylation of a series of allylic and benzylic alcohols was explored. Chemoselective reduction of a host of propargylic, propagylic/allylic, bis-allylic, allylic, and benzylic alcohols with Et(3)SiH was achieved in high yields with short reaction times. The same approach was successfully applied to couple representative propargylic and allylic alcohols with 1-phenyl-2-trimethylsilylacetylene. The recovery and reuse of the ionic liquid (IL) was gauged in a case study with minimal decrease in isolated yields after six cycles.

A facile and mild reduction procedure is reported for the preparation of chiral allylic and propargyl alcohols in high enantiomeric purity. Under optimized conditions, alkynyl and alkenyl ketones were reduced by TarB-NO2 and NaBH4 at 25 °C in 1 h to produce chiral propargyl and allylic alcohols with enantiomeric excesses and yields up to 99%. In the case of α,β-unsaturated alkenyl ketones, α-substituted cycloalkenones were reduced with up to 99% ee, while more substituted and acyclic derivatives exhibited lower induction. For α,β-ynones, it was found that highly branched aliphatic ynones were reduced with optimal induction up to 90% ee, while reduction of aromatic and linear aliphatic derivatives resulted in more modest enantioselectivity. Using the (L)-TarB-NO2 reagent derived from (L)-tartaric acid, we routinely obtained highly enantioenriched chiral allylic and propargyl alcohols with (R) configuration. Since previous models and a reduction of a saturated analogue predicted propargyl products of (S) configuration, a series of new mechanistic studies were conducted to determine the likely orientation of aromatic, alkenyl, and alkynyl ketones in the transition state.

In this work we presented several aspects regarding the possibility to use readily available propargylic alcohols as acyclic precursors to develop new stereoselective [Au(I)]-catalyzed cascade reactions for the synthesis of highly complex indole architectures. The use of indole-based propargylic alcohols of type 1 in a stereoselective [Au(I)]-catalyzed hydroindolynation/immiun trapping reactive sequence opened access to a new class of tetracyclic indolines, dihydropyranylindolines A and furoindolines B. An enantioselective protocol was futher explored in order to synthesize this molecules with high yields and ee. The suitability of propargylic alcohols in [Au(I)]-catalyzed cascade reactions was deeply investigated by developing cascade reactions in which was possible not only to synthesize the indole core but also to achieve a second functionalization. Aniline based propargylic alcohols 2 were found to be modular acyclic precursors for the synthesis of [1,2-a] azepinoindoles C. In describing this reactivity we additionally reported experimental evidences for an unprecedented NHCAu(I)-vinyl specie which in a chemoselective fashion, led to the annulation step, synthesizing the N1-C2-connected seven membered ring. The chemical flexibility of propargylic alcohols was further explored by changing the nature of the chemical surrounding with different preinstalled N-alkyl moiety in propargylic alcohols of type 3. Particularly, in the case of a primary alcohol, [Au(I)] catalysis was found to be prominent in the synthesis of a new class of [4,3-a]-oxazinoindoles D while the use of an allylic alcohol led to the first example of [Au(I)] catalyzed synthesis and enantioselective functionalization of this class of molecules (D*). With this work we established propargylic alcohols as excellent acyclic precursor to developed new [Au(I)]-catalyzed cascade reaction and providing new catalytic synthetic tools for the stereoselective synthesis of complex indole/indoline architectures.

Mononuclear complexes of the type [(p‐cymene)RuX(CO)(PR3)][OTf] (R=Ph, Cy; X=Cl, OTf) promote the direct catalytic propargylation of furan with propargyl alcohols. These precursors are generated in situ from [(p‐cymene)RuCl(OTf)(PR3)] by activation of the propargylic alcohol, leading to the carbonyl ligand formation via allenylidene and alkenyl‐hydroxycarbene intermediates. The generation of the catalytically active species requires a short initial thermal activation to induce decoordination of the p‐cymene ligand. The in situ generated catalyst has been applied to catalytic transformations of alkynes and propargylic alcohols: propargylation of furans, propargyl ether synthesis from internal and terminal propargylic alcohols with propargyl, homopropargyl and allyl alcohols, selective dimerization of phenylacetylene into E‐enyne, and propargyl alcohol rearrangement into α,β‐unsaturated aldehydes and ketones via the Meyer–Schuster rearrangement. The propargylation of propargylic alcohols containing internal CC bonds suggests an activation via the Nicholas‐type intermediate, the metal‐stabilized propargyl cation.

The authors report a general room-temperature procedure for the direct, regioselective substitution of the hydroxy group in allylic, propargylic and benzylic alcohols with sulfon­amides, carbamates and carboxamides, all of which are known to be relatively weak nucleophiles. A commercially available Bi(OTf)3/KPF6 catalytic system is used delivering the respective amides in moderate to excellent yields under mild reaction conditions. The definitive advantage of this method is the excellent generality, including the conversion of cyclic and acyclic, benzylic and non-benzylic allylic and even of tertiary propargylic alcohols and its regioselectivity - allylic alcohols have been found to be attacked in the sterically less hindered position, whereas in propargylic alcohols the nucleophile occupies the original position of the hydroxyl group.

A mild method for the replacement of a hydroxyl group by halogen: 3. the dichotomous behavior of α-haloenamines towards allylic and propargylic alcohols

The photodissociation of allyl and propargyl alcohols at 193 nm, which involves π−π* electronic transition and leads to the formation of OH, has been studied by using a laser photolysis−laser-induced fluorescence technique. The nascent OH radicals formed from both these molecules are found to be rotationally and vibrationally excited. The vibrational distributions are found to be similar, described by vibrational temperatures of 2070 ± 380 and 2130 ± 440 K for allyl and propargyl alcohols, respectively. The rotational temperatures of both v‘ ‘ = 0 and 1 levels of OH radicals from allyl alcohol are found to be almost the same, viz., 1960 ± 150 and 1900 ± 250 K, respectively, and close to the vibrational temperature. On the other hand, the rotational temperatures of OH radicals, 1760 ± 130 K at the v‘ ‘ = 0 level and 690 ± 120 K at the v‘ ‘ = 1 level, are very different from each other, in the case of propargyl alcohol. In both molecules, a significant part of the available energy is partitioned into the re...

The effects of saccharin and three kinds of aliphatic alcohols (n-propyl alcohol, allyl alcohol, propargyl alcohol) on the surface morphology and crystal orientation of electrodeposited nickel from a Watts bath (1 M NiSO4 + 0.21 M NiCl2 + 0.51 M H3 BO3 have been studied by means of electrochemical methods, scanning electron microscopy, energy-dispersive X-ray analysis and measurements of X-ray diffraction patterns. Saccharin and three kinds of aliphatic alcohols were adsorbed on the electrode and inhibited the reduction of nickel ion. The inhibitory effect on the reduction of nickel ion increased in the order n-propyl alcohol, allyl alcohol and propargyl alcohol. Large granular electrodeposits were obtained from the Watts bath in the absence of organic additives. When saccharin was added, fine-grained crystals were observed and the surface roughness was relatively small. When aliphatic alcohols were added, the size of surface morphological features became smaller in the order n-propyl alcohol, allyl alcohol and propargyl alcohol. Fine-grained, compact and smooth nickel electrodeposits, which had a preferred orientation with a (111) plane parallel to the surface, were obtained from the Watts bath containing both saccharin and propargyl alcohol.

A silver/DBU catalyst system was developed for the effective synthesis of cyclic carbonate and oxazolidinone from the reaction of CO2 with propargylic alcohols and propargylic amines, respectively, in high yields under mild conditions. It was found that the [3,3]-sigmatropic Meyer–Schuster-type rearrangement of the propargylic alcohol was mediated by CO2 in DMF to afford the corresponding α,β-unsaturated carbonyl compounds in high yields. The silver salt combined with the chiral Schiff base ligand could be applied to enantioselective chemical CO2 incorporation into various bispropargylic alcohols to produce the corresponding cyclic carbonate in high yields with high enantioselectivity. The absolute configuration was determined by VCD spectroscopy as well as by X-ray analysis. These products were found to be active for the aminolysis reaction to afford the corresponding carbamate derivatives in high yields without any loss of optical purity.

Substituted 4,4,5,5-tetraethoxy-2-pentyn-1-ols undergo stereospecific reduction to allylic and homoallylic alcohols under the right conditions. Hydrogenation over Lindlar's catalyst gave the corresponding (Z)-allylic alcohols in excellent yield provided potassium carbonate was added. Reduction was also achieved with lithium aluminum hydride, but the product appeared to be solvent and temperature dependent. In THF at -15 o C the corresponding (E)-allylic alcohols were formed, in better than 70% yield from secondary propargylic alcohols, but below 60% from tertiary ones; in refluxing diethyl ether the products were the corresponding 1-substituted derivatives of homoallylic alcohol (E)-4,5,5-triethoxypent-3-en-1-ol, obtained in 93% yield in the best case.

The enantioselective alkoxylation of -substituted aromatic nitroalkenes with propargyl alcohol in the presence of a chiral ligand, N-ethyl-N-{[(2S)-pyrrolidin-2-yl]methyl}ethanamine, results in the enantioselective synthesis of nitro-containing ethers with high yields and excellent enantioselectivity. This method accommodates a wide variety of arylthiols and nitroalkene substrates, producing the target compounds in moderate yields (up to 73%) and enantiomeric excess (up to 99% ee). The resulting compounds are valuable intermediates in organic synthesis, as they contain multiple reactive centers, such as terminal triple bond and nitro groups. Moreover, they serve as direct precursors for the synthesis of optically active propargylamines, which are crucial intermediates in the production of many biologically active molecules. Chiral unsaturated nitro compounds are important building blocks for the construction of complex synthetic materials. The addition of propargyl alcohol to unsaturated nitro compounds proceeds both regioselectively and enantioselectively. Experimental data demonstrate that good results can be achieved even with low catalyst loadings.

Deacylative allylation of nitroalkanes: unsymmetric bisallylation by a three-component coupling.

Copper(II)-catalyzed allylation of propargylic and allylic alcohols by allylsilanes: a facile synthesis of 1,5-enynes

This review article describes our recent efforts to develop environmentally benign transformations of allyl and propargyl alcohols via the 1,3-transposition of their hydroxyl groups using combined catalyst systems. This methodology allows for successful transformation under mild conditions, which has never been achieved using each catalyst. Representative examples of this methodology include the following three reactions. First, the combination of oxo-vanadium compounds and lipases resulted in the dynamic kinetic resolution of racemic allyl alcohols to give optically active allyl esters in high yields. Second, Mo-Au-Ag combination catalysis dramatically accelerated the rearrangement of diverse propargyl alcohols into α,β-unsaturated carbonyl compounds. Finally, the choice of suitable heteropoly acids for the rearrangement of propargyl alcohols led to the selective preparation of both (Z)- and (E)-enones.

Review: 24 refs.