Acetals palladium catalysis

CH2=C(OBn)CH2F, PdCl2(COD), CH3CN, it, 24 h, 89-100% yield. Protic acids can also be used to introduce this group, but the yields are sometimes lower. A primary alcohol can be protected in the presence of a secondary alcohol. This reagent also does not give cyclic acetals of 1,3-diols with palladium catalysis. 

Synthesis of isomeric chiral protected (63 )-6-amino-hexahydro-2,7-dioxopyrazolo[l,2- ]pyrazole-l-carboxylic acid 280 is shown in Scheme 36. Crude vinyl phosphonate 275, obtained by treatment of diethyl allyloxycarbonylmethyl-phosphonate with acetic anhydride and tetramethyl diaminomethane as a formaldehyde equivalent, was used in the Michael addition to chiral 4-(f-butoxycarbonylamino)pyrazolidin-3-one 272. The Michael addition is run in dichloro-methane followed by addition of f-butyl oxalyl chloride and 2 equiv of Huning s base in the same pot to provide 276 in 58% yield. The allyl ester is deprotected using palladium catalysis to give the corresponding acid 277, which is... 

The intramolecular palladium catalyzed ring closure of the tetrahydro-isoquinoline derivative depicted in 8.41. led to the formation of the aporphine derivative in good yield, which was then converted into racemic aporphine in three steps. In the ring closing step 20 mol% palladium acetate and 40 mol% tricyclohexylphosphine were used as catalyst. The removal of the hydroxyl group was also achieved by palladium catalysis through its conversion to triflate and the subsequent reduction with ammonium formate in the presence of palladium acetate and dppf.53... 

The present procedure uses palladium catalysis in the first step and in one of the second steps. These reactions occur under very mild conditions (room temperature) and the catalyst used is commercial palladium acetate. 

The EMCR has been extended from obtaining enantiomerically pure alcohols to obtaining such amines. Prochiral ketoximes were transformed to optically active amine acetates in a coupled CALB/palladium catalysis in the presence of an acyl donor at 1 atm hydrogen (Figure 18.15) (Choi, 2001). 

The desymmetrization of dicarbonate 206 was initiated by the addition of one equivalent of N-(3-butenyl) nosylamide 207 under palladium catalysis in the presence of Trost s chiral diphosphine ligand 205. When the first allylic substitution was completed, the reaction was warmed and the resulting intermediate 208 was treated in situ with one equivalent of a second nosylamide 209. Product 210 resulting from this double substitution reaction was submitted to a tandem intramolecular ROM/RCM to furnish key precursor 211, which was engaged in the final cyc-lization step by the reduction of the double bonds, followed by the HCl-promoted domino deprotection of the acetal and aminal formation. 

O/t/20-arylation of benzoic acids is often preferable to ortho-arylation of benzamides if conversion of the amide moiety to other functional groups is desired. However, only a few reports have dealt with the orf/io-functionalization of free benzoic acids due to challenges that involve such transformations. The reactions can be complicated by decarboxylation of the product and the starting material. Despite those difficulties, several methods for direct o/t/io-arylation of benzoic acids have been developed. Yu has shown that arylboronates are effective in arylation of benzoic acids under palladium catalysis [59], The reactions require the presence of palladium acetate catalyst, silver carbonate oxidant, and benzoquinone. Even more interestingly, the procedure is applicable to the arylation of unactivated sp3 C-H bonds in tertiary carboxylic acids such as pivalic acid (Scheme 13) if aryl iodide coupling partner is used. Aryl trifluoroborates can also be used [60],... 

Palladium(0)-catalysed coupling of an orf/to-halophenolic ether (thioether) with a terminal alkyne (or with an alkynylboronic ester ) and ring closure promoted with an electrophile - iodine has been most often used - is an excellent method to make both benzothiophenes °° ° and benzofurans. ortfto-AIkynyl-phenols can be comparably closed with palladium catalysis in the presence of copper(II) halides to give the corresponding 3-halo-benzofurans, ° and ortfto-alkynyl pyridin-2- and -3-yl acetates likewise ring close with iodine, generating furopyridines. ... 

Aryl-, alkenyl- and alkynylpalladium species readily undergo carbonylation reactions because carbon monoxide as a loosely bonded ligand can reversibly insert into any palladium-carbon bond [110]. Thus, 2-allyl-l-iodocyclopentene (148), under palladium catalysis, reacts with carbon monoxide in two modes, depending on the excess of carbon monoxide and the catalyst cocktail (Scheme 3-39) [110a]. With a slight excess (1.1 atm of CO) in the presence of [Pd(PPh3)4] in tetrahydrofuran, 148 cyclized with one CO insertion to yield 3-methylenebicyclo[3.3.0]oct-l(5)-en-2-one (152), and under 40 atm of CO with [Pd(PPh ,)2Cl2] in benzene/acetonitrile/methanol, methyl 2- 3 -(2 -oxobicyclo[3.3.0]oct-1 (5 )-enyl) acetate 149 after two CO insertions (Scheme 3-39). 

Oestxeich found that the direct arylation of indolines could be accomplished without over oxidation to the corresponding indole under palladium-catalysis with air (open flask), oxygen (balloon), or copper(II) acetate as the oxidant. Indolines can be unsubstituted or substituted as C2/C3 and the reaction performs well on gram scale (250, 18 examples, 18—90% isolated yield) (140L6020).A directed C2-functionalization/C7-alkenylation was discovered by Xu,Yi, and colleagues. With a rhodium catalyst, indole derivatives were functionalized with acetates at C2 (22 examples, 62—92% yield) the newly obtained products could be alkenylated at C7 with a rhodium/copper system (251,3 examples, 68—78% yield) (14CC6483). 

For example, reaction of methoxyallene with an allyHc alcohol under palladium catalysis yielded unsymmetrical mixed acetal 22a in 74% yield (Scheme 5(a)). Treatment of 22a with 10 mol% of Grubbs second generation catalyst 3, followed by add promoted aromatization yielded fiiran 12a in 79% isolated yield for the one-pot protocol. However, the nonpolar furan products were usually contaminated with (nonpolar) phosphine residues from the catalyst, which made the purification step problematic. Therefore, it was generally advantageous to purify the dihydrofuran intermediate prior to the aromatization step. In a similar manner to furans, allyftc sulfonamide 21a was converted to the N,0-acetal 23a in 63% yield under palladium catalysis. Then RCM followed by aromatization proceeded smoothly to provide the desired N-protected pyrrole 13a in 61% yield over two steps (Scheme 5(b)). This procedure can also be applied... 

Acetoxyindole derivatives have been prepared by the reaction of Af-benzylindole with (diacetoxyiodo)benzene catalysed by palladium acetate. Kinetic experiments suggest that palladation to produce intermediates, such as (60), is rate limiting. " Palladium catalysis, using a Josiphos ligand, has also been used to prepare (V-alkyltacrines, such as (61), by amination of 9-chlorotetrahydro-acridines. " ... 

It was shown that palladacydes 1 [3c, 24] prepared from palladium] I) acetate and tris(o-tolyl)- or trimesitylphosphine are excellent catalysts for the Heck coupHng of triflates and halides including certain aryl chlorides. In some of these cases, a possible involvement of oxidation states +II and +IV in the catalytic cycle has been considered [25]. Similarly, other palladacydes such as 3 [26e,h] or 6 [27] have been used in the Heck reactions (Figure 8.1) [24, 26, 28]. It has been proposed that, at least for NC palladacydes, the reaction proceeds through the classical phosphine-free Pd(0)/Pd(II) catalytic cycle and that the active catalysts are actually slowly formed palladium clusters [29]. Besides classical palladacydes, complexes with pincer-type ligands such as 2 [30] have become very popular in palladium catalysis [31]. 

The unsatuiated triflate 68 has been prepared and cross-coupled under palladium catalysis to a variety of vinjdic- and acet eniotributytin compounds to give products 69."... 

Anion Source for Palladium Catalysis. The reagent serves as a source of weakly coordinating anions in the palladium-catalyzed formation of mixed phenyl ureas, a known class of commercially available herbicides, using palladium(II) acetate, copper(II) toluenesulfonate, and 2,2 -dipyridyl as the catalyst system. Other studies have suggested that use of this reagent to form palladium salts may have useful applications in the reductive carbonylation of nitroaromatic compounds to give isocyanates via initial carbamate formation (eq 2). ... 

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