Reaction with propargyl ethers

The reaction of propargylic ethers proceeds through an addition-elimination pathway, which docs not involve the coppcr(III) intermediate. The stereochemical outcome varies with the nature of the halogen component of the Grignard reagent of RMgX6Sc. If the halogen is chloride, overall syn selectivity is obtained however, anti substitution results in the case of iodide. 

Reaction with Propargyl Halides. The indium-mediated coupling of propargyl bromide with a variety of imines and imine oxides afforded homo-propargylamine derivatives in aqueous media under mild conditions.78 Propargylation of glyoxylic oxime ether in the presence of a catalytic amount of palladium(O) complex and indium(I) iodide in aqueous media was also studied (Eq.11.47).79... 

Also studied was the effect of ether, which behaves as a retarder, on the polymerization. The retardation is most marked with the di- and trihalides and least with the monohalide and Zr (allyl) 4. In fact if large amounts of ether are present from the preparation, Zr(allyl)2Br2 shows hardly any activity at all. To avoid any possibility of contamination by ether, the halides in Table XI were prepared from pure ether-free Zr(allyl)4 in toluene by reaction with propargyl bromide. 

Another ingenious variation starts with 4-methoxypropargylamines 36 which are readily accessible via copper-catalyzed Mannich reaction of propargyl ethers U9>. The group R can again only be a hydrogen atom or methyl group. 

Cobalt-cycloheptyne complexes tethered with propargylic ethers were found to undergo also intermolecular as well as intramolecular [2+2+2] reactions to provide polycyclic benzocycloheptanes <03CC2936>. 

Stannylations.- Rh-catalyzed reaction of R SnH with propargyl ethers follows different courses depending on the organic residue R. 

Matsuda and co-workers found that silyl enol ethers of thiol esters are good nucleophiles in the reaction with propargylic-type esters to form p-alkynyl thiol esters in the presence of a catalytic amount of [Ir(cod)(POPh3)2]OTf 32 [37]. The acetoxy group of 29 was readily substituted at 25 °C to form thiol ester 31 with 93% yield by simply stirring together 29,4 equiv of silyl enol ether 30, and 32 (5 mol%) (Eq. 16). 

Scheme 3 Formation of allenes and/or alkynes by the reaction of Cp2ZrBu2 with propargyl ethers...

The intermolecular implementation of the above was reported by Tsuchimoto and Shirakawa et al [228]. In their work, 2-arylindoles were annulated with propargyl ethers with In(ONf)3 (ONf = nonaflate, C4F9SO3) as catalyst, resulting in a more convenient access to polycyclic heteroarenes (Figure 8.106). Bithiophenes and bifurans could also undergo the annulation reaction in an analogous fashion, albeit with lower yields. The structure of the major side product from the bithiophene... 

Scheme 4.8 CDC Reaction of p-diketones with propargylic ethers.

It has been revealed that the reaction of ketoximes with propargylic ethers affords, instead of pyrroles or their predecessors 0-vinyl oximes, 0-(3-alkoxy-2- -propenyl) ketoximes (Scheme 1.127) [297]. 

SCHEME 1.127 Reaction of ketoximes with propargylic ethers in the KOH/DMSO system. 

The flask was charged with 2.0 mol of dry, freshly distilled (note 1) methyl propargyl ether (VIII-6, Exp. 7), potassium iert.-butoxide (note 2) (5 g) was added with stirring and the mixture was heated under reflux. The reaction was... 

Ojj 1.5323, prepared from phenol, KOH in ethanol and propargyl bromide) was added and the mixture was heated at 60°C for 15 min. It was then poured into 200 ml of ice-water and the reaction products were extracted with diethyl ether. The ethereal extracts were washed with saturated NH Cl solution, dried over magnesium sulfate and then concentrated in a water-pump vacuum. There remained 9.5 g of 3 1 mixture... 

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