Phenyl propargyl ether

Another abnormal Claisen rearrangement is the product formed on heating phenyl propargyl ether. The normal product O-allenyl phenol rearranges by a [1, 5] hydrogen shift and then there is an electrocylic ring closure to give chromene which is the observed product. 

Sames et al. studied the cyclization of phenyl/propargyl ethers catalyzed by different metal salts since this Friedel-Crafts alkenylation had previously been reported to be catalyzed by metals such as Pd, Zr In and Sc [122-124] or even zeolites by hereogeneous catalysis [125]. In this preliminary research, the maximum yield of the desired product achieved by gold was only 6%, the best results being obtained with PtCl2 as catalyst [126]. 

Table 2 Isomer Distribution in the Cyclization of m-Substituted Phenyl Propargyl Ethers...

Figure 3.42 a General reaction scheme for the thermal Huisgen cycloaddition b the copper-catalyzed reaction between phenyl propargyl ether (phenyl 2-propynyl ether) and benzyl azide. The catalytic reaction is performed in the presence of a reductant (sodium ascorbate) and gives just one of the product isomers in high yield. 

Above 210°C, the reaction would result in the formation of an ever-increasing amount of the indanone by-product see Scheme 7.7. Interestingly, this side reaction turned out to be far from novel, as the mechanism behind forming 2-indanones on flash vacuum pyrolysis of phenyl propargyl ethers had already been thoroughly investigated and umaveled. °... 

Hansen, H.-J. and Schmid, H., Aromatic sigmatropic rearrangements, Chem. Brit., 5, 111, 1969. Trahanovsky, W.S. and Mullen, P.W., Formation of 2-indanone and benzocyclobutene from the pyrolysis of phenyl propargyl ether, J. Am. Chem. Soc., 94, 5911, 1972. 

Al-Sader, B.H. and Al-Fekri, D.M., On the mechanism of flash vacuum pyrolysis of phenyl propargyl ether. Intramolecular deuterium kinetic isotope effect on Claisen rearrangement, J. Org. Chem., 43, 3626, 1978. 

Phenol propargyl Phenol and propargyl ale. added to stirred PhjP in benzene (Nj) at ambient alcohol temp, and then E102CN=NC02Et added slowly. Reaction for 18h., to give phenyl propargyl ether. 

Deprotection. The title compound has been used for the deprotection of N-sulfonylaziridines (eq 28), substituted phenyl-propargyl ethers (eq 29), benzyl ethers in the presence of alkenes (eq 30), and phenylsilyl ethers in the presence of acid-sensitive groups. ... 

A mixture of phenyl propargyl ether, SeOg, and acetic acid refluxed 1 hr. in di-oxane >> phenol. Y 79%. F. e., also cleavage of allyl ethers, s. K. Kariyone and H. Yazawa, Tetrah. Let. 7979, 2885. 

A magnetically stirred solution of phenyl propargyl ether (40 mg, 0.30 mmol) in CH2CI2 (4 mL) maintained at 18 °C was treated with catalyst C (2.4 mg, 1 mol%). The resulting solution was stirred at 18 °C for 1 h and then concentrated under reduced pressure, and the ensuing yellow oil was subjected to flash column chromatography (silica gel, hexane) to give, after concentration of the appropriate firactions (Rf 0.3 in 1 49 v/v EtOAc/hexane), 2//-chromene (25 mg, 62%) as a clear, colorless oil. ... 

With the phenyl propargyl ether X (Ph-0-CH2-C=C-(p-tolyl)), the following reaction (a) is carried out... 

Phenyl propargyl ether (199) is isomerized in part to 2-indanone on low-pressure gas-phase pyrolysis ( 450 Q. The mechanism of this transformation (Scheme 10) is based on the work of Schmid and supported by employing the deuteriated propargyl ether (200), which yielded the appropriately labelled indanone (201). Pyrolysis studies on (202) and (203) have also been... 

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