Organocatalyzed highly stereoselective 1,4‐thia‐Michael addition of mercaptans to linear 2,4‐dienones and 2‐en‐4‐ynones was developed using Cinchona alkaloid‐based squaramides. Application of only 0.5–1 mol % loading afforded products in up to 98:2 e.r. and above 99:1 after a single recrystallization. The adducts of allyl mercaptan can be conveniently further transformed to new chiral 2‐substituted 2,5‐dihydrothiophenes by ring‐closing metathesis.
The selective copper‐catalyzed borylation of silylalkynes in the presence of a diboron reagent and methanol produced a variety of (Z)‐β‐(borylvinyl)silanes. The appropriate use of a selective ligand for copper allows the chemo‐, regio‐, and stereoselective monoborylation of silylalkynes. The β‐regioselectivity of an N‐heterocyclic carbene (NHC)‐copper catalyst was investigated by DFT calculations.
A practically simple and direct α‐alkylation of unactivated ketones using benzylic alcohols has been achieved. The in situ formed acetals are the key for the success of the reaction. The catalyst, silver hexafluoroantimonate(V) (AgSbF6) provides double activation by converting the ketone into an enol ether via acetal and generation of carbocationic center at the benzylic position of the benzylic alcohol. The alcohols include benzylic propargyl alcohols, cinnamyl alcohols, and diarylmethanols.
A cost‐effective, operationally simple and eco‐compatible protocol for the one‐pot synthesis of photochromic pyrans by the reaction of propargyl alcohols as well as propargyl ethers with differently substituted phenols under ambient atmosphere in aqueous medium has been developed using β‐cyclodextrin hydrate as an efficient, recyclable and stable catalyst. This is the first report where β‐cyclodextrin hydrate acted as a catalyst for an organic transformation but β‐cyclodextrin alone failed.
A quinine‐derived thiourea catalysed the enantioselective addition of 4‐substituted pyrazolones to isatin‐derived ketimines, providing a variety of aminooxindole‐pyrazolone adducts containing congested vicinal tetrasubstituted stereocentres with excellent outcomes (up to 98% yield, >20:1 dr and 98% ee).
We report a triple vinylogous cascade reaction, yielding valuable spiro‐oxindolic cyclohexane derivatives. The three‐component domino process proceeds by way of a catalyzed Michael/1,6‐addition/vinylogous aldol sequence affording the products with six stereogenic centers and very high control over the stereochemistry. The chemistry is based on a rare example of asymmetric 1,6‐addition to linear 2,4‐dienals proceeding with complete δ‐site selectivity. Key to the reaction development was a directing group positioned at the β‐dienal position, which was essential for achieving highly predictable reaction outcomes.
We describe here a convenient and mild, carbon monoxide gas‐free palladium‐catalyzed procedure to obtain N‐substituted phthalimides with molybdenum hexacarbonyl as carbon monoxide precursor. These conditions tolerate a number of functional groups on the benzene ring as well as a number of amines and give the corresponding phthalimides in good to excellent yields.
The asymmetric conjugate 1,4‐addition of arylboronic acids to α,β‐unsaturated carbonyl compounds is an extremely versatile and widely used organic transformation. While the rhodium(I)‐catalysed reaction has been thoroughly explored, the asymmetric palladium‐catalysed protocol is far less developed and understood, particularly with acyclic enones as substrates. Herein, we report the systematic evaluation of a series of metallacycles for this reaction and the conjugate addition of arylboronic acids to a wide range of α,β‐unsaturated enones, catalysed by an easily accessible and robust chiral phosphapalladacycle in high yields and enantioselectivities.
Zinc‐catalyzed 1,4‐oxofluorinations of 3‐en‐1‐ynamides with Selectfluor in acetonitrile/water proceeded with high regio‐ and stereoselectivity, giving E‐configured γ‐fluoro‐α,β‐unsaturated amides efficiently. Our control experiments indicate that kinetically unstable C‐bound zinc dienolates are chemically reactive to undergo SE2′‐electrophilic fluorinations whereas the detectable O‐bound dienolates preferably undergo protodemetalation reactions instead.
A novel copper‐catalyzed oxidative alkylation of α‐amino carbonyl compounds with ethers has been established for the selective synthesis of α‐etherized α‐amino carbonyl compounds. This oxidative alkylation is achieved by dual C(sp3) H bond oxidative cross‐coupling, and its scope is expanded to α‐amino ketones, α‐amino esters and α‐amino amides.
