Carbamates Palladium chloride

C(l) in 355 is in the oxidation state of an aldehyde or a ketone in 1-alkylated products. The necessary solvolytic attack of the enol carbamate double bond requires substoichio-metric amounts of a catalyst such as mercuric acetate or palladium chloride and one equivalent of acid (e.g. methanesulphonic acid) for binding the liberated diisopropylamine. 

Benzyl esters and carbamates in the presence of other easily reducible groups such as aryl bromides, cyclopropanes, and alkenes are selectively cleaved with tri-ethylsilane and palladium chloride. ... 

Metal-catalysed cyclization is an increasingly important method of synthesis (reviews [B-4I, 2998, 3069, 3501, 3505 ). Bis(acetonitrile)dichloropalladium promotes cyclization of an alkynyl carbamate with epoxypropane and a vinyl chloride [3438] an alkynylaniline is converted into an indole by heating with a palladium chloride-triphenylphosphine catalyst [3631]. Mercury(II) acetate is an effective promotor of the cyclization of the alkenylaniline (37.2) to a reduced carbazole [3861]. 

Kostic et al. recently reported the use of various palladium(II) aqua complexes as catalysts for the hydration of nitriles.456 crossrefil. 34 Reactivity of coordination These complexes, some of which are shown in Figure 36, also catalyze hydrolytic cleavage of peptides, decomposition of urea to carbon dioxide and ammonia, and alcoholysis of urea to ammonia and various carbamate esters.420-424, 427,429,456,457 Qggj-jy palladium(II) aqua complexes are versatile catalysts for hydrolytic reactions. Their catalytic properties arise from the presence of labile water or other solvent ligands which can be displaced by a substrate. In many cases the coordinated substrate becomes activated toward nucleophilic additions of water/hydroxide or alcohols. New palladium(II) complexes cis-[Pd(dtod)Cl2] and c - Pd(dtod)(sol)2]2+ contain the bidentate ligand 3,6-dithiaoctane-l,8-diol (dtod) and unidentate ligands, chloride anions, or the solvent (sol) molecules. The latter complex is an efficient catalyst for the hydration and methanolysis of nitriles, reactions shown in Equation (3) 435... 

Primary aliphatic or aromatic amines RNH2 are converted into carbamates RNHCC Et on treatment with carbon monoxide and di-t-butyl peroxide in the presence of palladium(II) chloride and copper(II) chloride357. Carbamic esters 304 and 305 are also obtained from aliphatic amines and ortho carbonates (R30)4C358. Vinyl carbamates R12NC02CH=CHR2 are produced from secondary aliphatic amines, acetylenes R2C=CH (R2 = Bu or Ph) and carbon dioxide in the presence of ruthenium(III) chloride359. 

Pd(0)/phosphine complexes, or their precursors, in the presence of a suitable co-base, have also been shown to promote, in good yields (66-100%), the formation of allylic carbamates from various primary and secondary aliphatic amines, pressurized C02 and allylic chlorides, in THF, at ambient temperature [87a]. The choice of the added co-base (Base), used for generating the carbamate salt RR NC02 (BaseH)+, was found to be critical for high yields of O-allylic urethanes. The use of a guanidine (CyTMG) or amidine (DBU) base was optimal for this system (see also Section 6.3.1). ft is assumed that this chemistry passes catalytically through a mechanism similar to that illustrated in Scheme 6.19. This involves nucleophilic attack by carbamate anion on a (tt-allyl) palladium species, formed by the oxidative addition of the allylic chloride to a palladium(O) intermediate. 

Scheme 6.19 Palladium-catalyzed generation of O-allylic carbamates from amines, C02, and allylic chlorides.

A new copper-catalyzed reaction involving imines, acid chlorides, and alkynes has been applied to the synthesis of propargyl amides 160 in a single operation by Arndtsen and co-workers. The same method allows the synthesis of N-carbamate-protected propargylamines [149]. a-Substituted amides 161 may also be prepared under palladium catalysis by substituting alkynes for vinyltin (Scheme 8.71) [150]. 

Palladium(II) catalysis (0.01-0.04 equiv) is more effective and leads to higher selectivity than mercury(II) catalysis912. With bis(acetonitrile)palladium(II) chloride [Pd(CH3CN)2CI2] as catalyst the efficiency decreases in the order carbamates > allylic acetates > carbonates. 

The palladium(II)-catalyzed oxidative aminocarbonylation of 0-(2-propenyl)-Ar-tosyl carbamates 12 was achieved under acidic buffer conditions, although the reaction was very sluggish, or, preferably in the presence of acetate ion and methyl orthoacetate, which suppresses palladium(II) chloride consuming side reactions114. Substitution at C-l led to the prevalent formation of the trans-4,5-disubstituted 1,3-oxazolidin-2-ones 13 (NMR). 

G-Allylic urethanes and carbonates are afforded from amines/alcohols, carbon dioxide and allylic chlorides by palladium catalysed reaction in the presence of an organobase. The choice of added base in the generation of carbamates/carbonates was critical for high yields... 

Ragaini and associates found that fluorides can promote the palladium-phe-nanthroline catalyzed carbonylation of nitroarenes to carbamates. The effect was more evident on the rate of the reaction at short reaction times, but a positive effect on selectivity is also observed under certain conditions. The effect was observed even under conditions in which chloride inhibits the reaction. The reason for these results might be that fluoride can avoid the formation of inactivating byproducts that deactivate the catalyst. Additionally, tetraethylammonium fluoride was found to be better than sodium fluoride. 

Willis has similarly noted that indoles can be prepared via the cascade coupling of the aryl-halide and vinyl-triflate bonds in styrene 21 with primary amines (Scheme 6.41). Despite the fact that two different types of C—X bonds must be activated, this process proceeds with a single palladium catalyst (Pd2dba3/Xantphos), and a range of primary amines, carbamates and amides. More recently, even vinyl chlorides were found to participate in this coupling reaction [53]. 

Han has comprehensively reviewed the use of nickel catalysts for the Suzuki-Miyaura cross-coupling reaction/ and found that the nickel mediated process can tolerate a broad range of aryl electrophiles, for example, sulfamates, carbamates, carboxylates, ethers, carbonates, phosphoramides, phosphonium salts, phosphates, phenols, and a broad range of alkyl substrates including both secondary and primary alkyl iodides, bromides, and chlorides. Many of these electrophiles have been found to be incompatible with traditional palladium catalysed processes. 

Using the palladium(II) chloride system, the reaction involving secondary amines was found to give mixtures of carbamate ester and an oxamate ester resulting from double carbonylation. Analogous carbonylations of alcohols can lead to a range of products, including dialkyl carbonates, oxalates, and succinates. ... 

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