Arylation of vinyl ethers

Heck arylation of vinyl ether 160 with 4-bromoacetophenone and 1-bromonaphthalene, respectively, catalyzed by [Pd(C3Hs)Cl]2 and using Tedicyp, as a ligand, gave dioxepanes 163 and 164 together with a mixture of regioisomeric aryl vinyl ethers 161 and 162 (Scheme 44) <2006EJ0765>. 

Palladium-catalysed multiple and asymmetric arylations of vinyl ethers... 

PALLADIUM-CATALYSED MULTIPLE AND ASYMMETRIC ARYLATIONS OF VINYL ETHERS CARRYING CO-ORDINATING NITROGEN AUXILIARIES SYNTHESIS OF ARYLATED KETONES AND ALDEHYDES... 

Table 5.4 Heck arylation of vinyl ethers by aryl bromides in [bmim][BF4].

Herrmann s palladacycle = [trans-di(p-acetato)bis[o-(di-o-tolyl-phosphino)benzyl]dipalladium (II)] Scheme 3.2. Microwave-assisted double-Heck arylations of vinyl ethers. 

Andersson, C.M. and Hallberg, A. (1988) Regioselective palladium-catalyzed arylation of vinyl ethers with 4-nitrophenyl triflate. Control by addition of halide ions. J. Org. Chem., S3, 2112-4. 

Datta, G.K., von Schenck, H., Hallberg, A. and Larhed, M. (2006) Selective terminal Heck arylation of vinyl ethers with aryl chlorides a combined exf>erimental- omputational approach including synthesis of betaxolol. J. Org. Chem., 71, 3896-903. 

Nilsson, R, Lathed, M. and Hallberg, A. (2001) Highly regioseleclive, sequential, and multiple palladium-catal5 ed arylations of vinyl ethers carrying a coordinating auxiliary an example of a Heck triarylation process. J. Am. Chem. Soc., 123, 8217-25. 

Hallberg s group deliberately introduced y6-amino tethers for the /3-selective arylation of vinyl ethers. They further extended this system to chiral substrates for diastereoselec-tive arylation processes. Similar to their systems, Badone introduced /3-phosphino tethers for the /3-selective arylation of vinyl ethers. Tamaru has reported carbamate directing... 

Figure 7.9 Amino-directed -selective arylation of vinyl ethers.

Favoring the jS-regioselectivity of the Heck reaction with electron-rich alkenes is not so simple. In 1988, Andersson and Hallberg observed that the type of halide coordinating to the metal center had a profound influence on the regioselectivity, chloride favoring the formation of the )S-alkene when using vinyl ethers [214,215]. Scheme 4.65 shows the most relevant results in the hterature toward the p-reg-ioselective arylation of vinyl ethers. 

The first palladium-catalyzed formation of aryl alkyl ethers in an intermolecular fashion occurred between activated aryl halides and alkoxides (Equation (28)), and the first formation of vinyl ethers occurred between activated vinyl halides and tin alkoxides (Equation (29)). Reactions of activated chloro- and bromoarenes with NaO-Z-Bu to form /-butyl aryl ethers occurred in the presence of palladium and DPPF as catalyst,107 while reactions of activated aryl halides with alcohols that could undergo /3-hydrogen elimination occurred in the presence of palladium and BINAP as catalyst.110 Reactions of NaO-/-Bu with unactivated aryl halides gave only modest yields of ether when catalyzed by aromatic bisphosphines.110 Similar chemistry occurred in the presence of nickel catalysts. In fact, nickel catalysts produced higher yields of silyl aryl ethers than palladium catalysts.108 The formation of diaryl ethers from activated aryl halides in the presence of palladium catalysts bearing DPPF or a CF3-subsituted DPPF was also reported 109... 

Vinyl ethers yield acylated vinyl ethers when they are reacted with aroyl chlorides or 3-thienylcarbo-nyl chloride, triethylamine and a palladium acetate catalyst at 60-70 C (equation 43).103 The products of this reaction are useful 1,3-dicaibonyl equivalents. At higher temperatures the reaction yields arylated vinyl ethers. It is interesting that the acylations of vinyl ethers are regioselective while the direct aryla-tions are usually not.104... 

Aryl cation chemistry allows a double functionalization of vinyl ethers in a three-component reaction, as depicted in Scheme 3.30. In this case, a 3-arylacetal (e.g., 47) was synthesized after the initial addition of the 4-hydroxyphenyl cation onto ethyl vinyl ether, followed by trapping with the nucleophilic solvent MeOH [77]. For related arylation reactions, see Chapter 10. 

Stable A -l,3,4-oxadiazolines 116 have been synthesized from HFA and disubstituted diazomethanes (252). Thermal elimination of N2 yields oxi-ranes 117b if both substituents are aryl, and vinyl ethers 117a in the case of methyl-substituted diazomethanes (252). 

The reaction of vinyl ethers with tropylium salts was investigated by Volpin s school in different media There seems to be no doubt that the tropylium ion readily adds on to the double bond at the CH2 site. Bawn et al. found aryl groups in poly(vinyl ethers) prepared with trityl salts and no evidence for the formation of triphenylmethane among the products. It seems therefore, that initiation in these systems takes place according to a simple electrophilic addition ... 

The C(0)-0 bond length in esters is significantly shorter than the C(sp )-0 bond of aryl or vinyl ethers. In a study of the geometry of thioesters in crystal structures by Zacharias et al. [27] it was found that the bond length does not differ from that of the corresponding bond in aryl and vinyl monosulfides (O 1.336 [21] vs. 1.367 A S 1.767 vs. 1.763 A [27]). This suggests that there is more electron delocal-... 

Aryl and Vinyl Ethers. Aryl alkyl ethers give rise to two strong bands an asymmetric C—O—C stretch near 1250 cm and a symmetric stretch near 1040 cm , as seen in the spectrum of anisole (Fig. 2.34). Vinyl alkyl ethers also give two bands one strong band assigned to an asymmetric stretching vibration at about 1220 cm and one very weak band due to a symmetric stretch at about 850 cm ... 

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