Palladium-catalyzed coupling of haloalkynes with allyl acetate: a regio- and stereoselective synthesis of (Z)-β-haloenol acetates

A Pd-catalyzed coupling of haloalkynes with allyl acetate has been reported, providing a convenient method for the stereoselective synthesis of (Z)-β-haloenol acetates in good yields. The synthetic utility of this method is demonstrated by the formation of functionalized enol acetates via the Suzuki-Miyaura or Sonogashira coupling of the resulting (Z)-β-haloenol acetate products.     

Silver-promoted trans-hydrofluorination of ynamides: a regio- and stereoselective approach to (Z)-α-fluoroenamides

A highly regio- and stereoselective trans-hydrofluorination of N-sulfonyl ynamides has been realized with AgF as the fluorination reagent, affording (Z)-α-fluoroenamides in good to excellent yields. The reaction proceeds under mild reaction conditions and shows good functional group compatibility.     

Addition of TMS-substituted oxiranyl anions to acylsilanes. A highly stereoselective approach to tetrasubstituted (Z)-β-hydroxy-α-TMS silyl enol ethers

A highly stereoselective approach to novel tetrasubstituted (Z)-β-hydroxy-α-TMS silyl enol ethers is described. The reaction proceeds via a sequential addition/[1,2]-Brook rearrangement/epoxide-opening process of TMS-substituted oxiranyl anions with acylsilanes.     

A highly stereoselective approach to tetrasubstituted (E)-β-hydroxy silyl enol ethers by addition of aryl-substituted oxiranyl anions to acylsilanes

A highly stereoselective approach to tetrasubstituted (E)-β-hydroxy silyl enol ethers is described. The reaction proceeds via a sequential addition/[1,2]-Brook rearrangement/epoxide-opening process of aryl-substituted oxiranyl anions with acylsilanes.     

(E)- and (Z)-β-borylallylsilanes by alkyne silaboration followed by regio- and stereoselective double-bond migration

Double take: β-Borylallylsilanes have been synthesized by the regioselective silaboration of terminal alkynes followed by palladium-catalyzed double-bond migration of the resulting β-borylalkenylsilanes. The stereoselectivity of the double-bond migration can be controlled by additives, thus leading to the stereocomplementary synthesis of (E)- and (Z)-β-borylallylsilanes.     

Gallium(III)-catalysed bromocyanation of alkynes: regio- and stereoselective synthesis of β-bromo-α,β-unsaturated nitriles

Treatment of arylacetylenes and cyanogen bromide in ClCH(2)CH(2)Cl with a catalytic amount of GaCl(3) afforded (Z)-β-bromoacrylonitriles with high regio- and stereoselectivity.     

Formal synthesis of (±) —quebrachamine through regio- and stereoselective hydrocyanation of arylallene

This article describes the formal synthesis of quebrachamine based on regio- and stereoselective hydrocyanation of 1,3-disubstituted allenes. Allenyl CC double bonds are effectively discriminated through Ni-catalyzed hydrocyanation and a CN group is utilized as a synthon of piperidine ring. Several steps from HCN adduct afforded known intermediates to quebrachamine.     

TiCl4-mediated olefination of aldehydes with acetic acid and alkyl acetates: a stereoselective approach to (E)-α,β-unsaturated carboxylic acids and esters

A new method has been developed for the preparation of α,β-unsaturated carboxylic acids and corresponding esters with (E)-stereoselectivity via the TiCl₄-mediated olefination of aldehydes. The method, which uses readily available acetic acid or its alkyl esters as active methylene partners, is more flexible and complementary to conventional routes in the preparation of (E)-cinnamic acid derivatives.     

(E) Enol ethers from the stereoselective reduction of α-alkoxy-β-ketophosphonates and Wittig type reaction

When α-alkoxy-β-ketophosphonates, prepared by the Rh(II) mediated insertion reaction of α-diazo-β-ketophosphonates into the OH bond of primary alcohols, were reduced either by NaBH₄ in the presence of CaCl₂ or by DIBAL, they respectively gave the corresponding anti or syn stereomeric hydroxyphosphonates with pronounced to complete stereoselectivity. Submitted to the action of potassium tert-butoxyde, syn isomers led to the corresponding pure (E) enol ethers in moderate to good yields. Under the same conditions anti isomers led to a mixture of (Z) and (E) enol ethers in rather poor yields. The sequence was applied to the preparation of some allyl-vinyl ethers with a (E) configuration for the vinylic double bond.     

Palladium-catalyzed stereoconvergent formylation of (E/Z)-β-bromo-β-fluorostyrenes: straightforward access to (Z)-α-fluorocinnamic aldehydes and (Z)-β-fluorocinnamic alcohols

We report here the stereoconvergent formylation of (E/Z)-β-bromo-β-fluorostyrene mixtures with carbon monoxide and sodium formate catalyzed by palladium. Optimization of reaction conditions leads to the corresponding pure (Z)-α-fluorocinnamaldehydes in good yields. The reaction was extended to styrenes bearing electro-attracting or electro-donating groups. The obtained α-fluoroaldehydes were smoothly reduced to the corresponding (Z)-β-fluorocinnamic alcohol by NaBH(4). The reaction could be performed on functionalized substrates as demonstrated by the access to the glucoside of β-fluoroconiferyl alcohol, (Z)-β-fluoroconiferin, a strong inhibitor of lignin polymerization.     

Chemoselective cross-coupling of terminal propargylamines with (het)aroyl chlorides: synthesis of β-aminoacetylenic ketones bearing aromatic and heteroaromatic substituents

Russian Chemical Bulletin - Terminal secondary 4-chlorophenyl propargylamines, synthesized by addition of acetylene to N-(4-chlorophenyl)ketimines (ButOK, DMSO, 20–25 °C) in 76–93%...     

Total synthesis of (±)-nicolaioidesin B via a highly regio- and diastereoselective Diels–Alder reaction

The total synthesis of (±)-nicolaioidesin B, a natural product that shows preferential cytotoxicity against pancreatic cancer cells under nutrient starvation conditions, is achieved. The key step is a thermally-induced, highly regio- and diastereoselective Diels–Alder reaction between (E)-N-methoxy-N-methylcinnamide and ocimene under solvent-free conditions.     

Total synthesis of (−)-funebrine via Au-catalyzed regio- and stereoselective γ-butyrolactonization of allenylsilane

The stereoselective total synthesis of (−)-funebrine from 2-butyn-1-ol was described. The crucial steps in the synthesis involved the stereoselective enolate Claisen rearrangement of the (S)-α-acyloxy-α-alkynylsilane 8, the Au-catalyzed regio- and stereoselective lactonization of the allenylsilane 7, and the Paal-Knorr pyrrole condensation using an unsymmetrical 1,4-diketone 4b.     

Efficient approach to allylated quinolines via palladium-catalyzed cyclization–allylation of 1-azido-2-(2-propynyl) benzenes with allyl methyl carbonate

The palladium-catalyzed cyclization–allylation reaction of ortho-azido propynylbenzenes 1 and allyl methyl carbonate 2d gives the corresponding allylated quinolines in moderate to good yields. The reaction of 1-azido-2-(2-propynyl)benzene 1a proceeds smoothly with 10 mol % Pd(PPh₃)₄ and 5 equiv K₃PO₄ or NaOAc in DMF at 100 °C to afford 3,4-diallylquinoline 3a in 69% yield in the case of R² = H and 3-allylquinoline 4 in 67% yield in the case of R² ≠ H.     

Chromium-mediated stereoselective synthesis of carbohydrate-derived (E)-α,β-unsaturated esters or amides

A chromium-mediated novel synthesis of carbohydrate-derived di- and trisubstituted (E)-α,β-unsaturated esters or amides from a range of dichloroesters or amides and a variety of sugar aldehydes is reported. The process took place with total stereoselectivity and in high yields. A mechanism based on a sequential chromium-promoted aldol-type reaction and a completely stereoselective β-elimination reaction is proposed to explain these results.     

Palladium-catalyzed allylic nucleophilic substitution reactions of (E)-γ-acetoxy-α,β-unsaturated p-tolylsulfoxides

Regio- and diastereoselective nucleophilic allylic substitutions of optically pure (E)-γ-acetoxy-α,β-unsaturated p-tolylsulfoxides 2 and 3 with sodium dimethyl malonate have been carried out. The reactivity of these substrates is controlled by both the chiral sulfinyl group and the size of the alkyl group attached at the γ-terminus of the allylic system. This process constitutes an example of palladium-mediated resolution of a 1:1 mixture of acetates 2 and 3.     

A highly stereoselective pinacolization of aromatic and α, β-unsaturated aldehydes.dta mediated by titanium(III)-magnesium(II) complex

Reduction of Cp₂TiCl₂ withsec-BuMgCl in THF gave a greenish deep brown solution which has been found to promote the reductive homocoupling of aromatic and α, β-unsaturated aldehydes to yield symmetrical 1, 2-diols with highthreo-selectivity.     

Hydroboration of (1R)-(+)-α-pinene and (1S)-(−)-β-pinene with B10H12(SMe2)2: a straightforward approach to the preparation of optically active 6-(alkyl)-nido-B10H13 derivatives

In separate three-step, one-pot procedures, the known polyhedral boron hydride arachno-6,9-(Me₂S)₂B₁₀H₁₂ is combined with α- or β-pinene to produce the optically active boranes (−)-6-(α-pinanyl)–B₁₀H₁₃ (1) and (−)-6-(β-pinanyl)–B₁₀H₁₃ (2), respectively, as crystalline solids in good yields.     

A stereoselective approach to the angucyclinone antibiotics: A total synthesis of (±)-urdamycinone B

A stereoselective chiral Lewis acid promoted reaction of siloxydiene (±)-13 and dienophile complex 18, gave a 4:1 mixture of urdamycinone B (1) and its C-3 epimer (24) in several steps in 12% overall yield. Separation of these products was achieved by high performance liquid chromatography (HPLC).