Ethers, allyl palladium catalysis

The synthesis of thiepins 14 was unsuccessful in the case of R1 = i-Pr,79 but if the substituents in the ortho positions to sulfur arc /erf-butyl, then thiepin 14 (R1 = t-Bu R2 = Me) can be isolated in 99% yield.80 Rearrangement of diazo compound 13 (R1 = t-Bu R2 = H), which does not contain the methyl group in position 4, catalyzed by dimeric ( y3-allyl)chloropalladium gives, however, the corresponding e.w-methylene compound. The thiepin 14 (R1 = t-Bu, R2 = H) can be obtained in low yield (13 %) by treatment of the diazo compound with anhydrous hydrogen chloride in diethyl ether at — 20 C.13 In contrast, the ethyl thiepin-3,5-or -4,5-dicarboxylates can be prepared by the palladium catalysis method in satisfying yields.81... 

Allyl carbonates can be cleaved by nucleophiles under palladium(O) catalysis. Allyl carbonates have been proposed for side-chain protection of serine and threonine, and their stability under conditions of /VT moc or /V-Boc deprotection has been demonstrated [107]. Prolonged treatment with nucleophiles (e.g., 20% piperidine in DMF, 24 h) can, however, lead to deprotection of Alloc-protected phenols [108,109]. Carbohydrates [110], tyrosine derivatives [107], and other phenols have been protected as allyl ethers, and deprotection could be achieved by palladium-mediated allylic substitution (Entry 9, Table 7.8). 9-Fluorenyl carbonates have been used as protected intermediates for the solid-phase synthesis of oligosaccharides [111]. Deprotection was achieved by treatment with NEt3/DCM (8 2) at room temperature. 

Kuntz, E., Amgoune, A., Lucas, C. and Godard, G. (2006) Palladium TPPTS catalyst in water C-allylation of phenol and guaiacol with allyl alcohol and novel isomerisation of allyl ethers of phenol and guaiacol./. Mol. Catal. A Chem., 244,124. Kuntz, E.G. (1987) Homogeneous catalysis. .. in water. Chemtech, 17, 570. Cornils, B. (1999) Bulk and fine chemicals via aqueous biphasic catalysis. /. Mol. Catal. A Chem., 143, 1. 

Allyloxypyrimidine largely resists rearrangement even at 200 C. However, allylic cyclopentenyl 2-pyrimidinyl ethers 879 can be rearranged on catalysis by tetrakis(tri-isopropyl phosphite)palladium (Scheme 95). 

Joint catalysis by tin(IV) chloride and zinc chloride induces coupling of the acetal 114 with the alkyne 115 to give the propargyl ether 116. Allyl halides condense with terminal alkynes in DMF in the presence of copper(I) iodide, potassium carbonate and tetrabutylammonium chloride under phase-transfer conditions to afford eneynes, e.g. equation 19. Palladium-catalysed coupling reactions of 1-bromoallenes with terminal acetylenes have been reported for the first time thus acetylene and the allenes 117 (R R = Me or Et) in triethylamine in the presence of tetrakis(triphenylphosphine)palladium and... 

The Stille reaction in some cases (reactions with reactive iodoarenes, etc.) benefits from phosphine-free catalysis. The use of phosphine-free complexes, such as Pd(dba)2, PdCl2(MeCN)2. [(i7 -allyl)PdCl]2, or even simple palladium salts, allows one to perform the reactions under milder conditions, at lower temperatures, in less polar solvents (acetone, THF, ether, benzene), and with lower amounts of catalyst to achieve higher TON values. 

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