Triflates carbon monoxide reactions

The palladium-catalyzed system can be extended to the acylation of siloxycyclopropanes with aroyl chloride/carbon monoxide or aryl triflate/carbon monoxide, which gives 1,4-diketones. Contrary to the case of doubly oxygen-substituted cyclopropanes vide infra), the acylation of 1-siloxycyclopropanes is restricted to aroyl chlorides and is not applicable to aliphatic or a, -unsaturated acyl chlorides. For the reactions with aryl triflates, tetrakis(triphenylphos-phane)palladium(O) is used as catalyst, while the reactions with aroyl chlorides employ bis(triphenylphosphane)palladium(II) chloride and ( / -allyl)chloropalladium dimer/triphenyl phosphite as catalysts. In these reactions, aroylpalladium(II) species may undergo ring opening of the siloxycyclopropanes. 

Soderberg and coworkers have developed a palladium-phosphine-catalyzed reductive iV-het-eroannulation of 2-nitrostyrenes forming indoles in good yields.85 For example, reaction of 6-bromo-2-nitrostyrene with carbon monoxide in the presence of a catalytic amount of palladium diacetate (6 mol%) and triphenylphosphine (24 mol%) in acetonitrile at 70 °C, gives 4-bromoindole in 86% yield (Eq. 10.62). Several functional groups, such as esters, ethers, bromides, triflates, and additional nitro groups, have been shown to be compatible with the reaction conditions. 

Like most aryl halides, furyl halides and furyl triflates have been coupled with a variety of organostannanes including alkenyl, aryl, and heteroaryl stannanes in the presence of catalytic palladium. Carbamoylstannane 66 was prepared by treating lithiated piperidine with carbon monoxide and tributyltin chloride sequentially. The Stille reaction of 66 and 3-bromofuran then gave rise to amide 67 [61]. In another example, lithiation of 4,4-dimethyl-2-oxazoline followed by quenching with MesSnCl resulted in 2-(tributylstannyl)-4,4-dimethyl-2-oxazoline (68) in 70-80% yield [62], Subsequent Stille reaction of 68 with 3-bromofuran afforded 2-(3 -furyl)-4,4-dimethyl-2-oxazoline (69). 

When carbon monoxide is bubbled through a methanol solution of (dppp)Pd(triflate)2 a carbomethoxy-palladium species is formed, which can undergo insertion of alkenes and hence this is a feasible alternative initiation route to chain-growth polymerisation (Figure 12.4) [13], To ensure a clean formation of the carbomethoxy species, however, exclusion of water is a prerequisite. If during the preparation water was present the formation of a palladium hydride complex (dppp)PdFT was observed (reaction (1), Figure 12.2). 

On the other hand, the use of [Rh(CO)2Cl]2 as a catalyst results in ring opening of the siloxycyclopropanes 13 to the silyl enol ethers 14 with high stereoselectivity [10]. The 2-siloxyrhodacyclobutane 15a is proposed to undergo j8-elimination to give jr-allylrhodium 16a followed by reductive elimination to the silyl enol ether 14a. 1-Trimethylsiloxybicyclo[n.l.0]alkanes serve as / -metallo-carbonyl compounds via desilylation with a variety of transition metals [11]. The palladium-catalyzed reaction of the siloxycyclopropanes 17 under carbon monoxide in chloroform provides a route to the 4-keto pimelates 18. In the presence of aryl triflates, the 1,4-dicarbonyl compounds 19 are... 

Pyrrolo-benzoxazepine 402 (Scheme 84, Section 5.2.1.1) gives ester 403 through the triflate intermediate by reaction with carbon monoxide and methanol in the presence of tetrakis(triphenylphosphine)palladium (1996JMC3435). 

Vinylic triflates such as 244 also allow the introduction of C-bonded substituents reaction with dilithium diallylcopper cyanide gives the 1,4-diene 245 in 76% yield,232 and Stille coupling with tributylvinyltin and carbon monoxide in the presence of palladium(O) produces the dienone 246 in 71% yield.233 234... 

Initially the Pd(0) complex oxidatively adds to enol triflate 6 to form a vinyl-Pd(II) species. Carbon monoxide then inserts into the new Pd—C o-bond to yield a palladium(ll)-acyl complex which captures methanol. The methanolysis step is formally a reductive elimination reaction in which the Pd(0) catalyst is regenerated to propagate the catalytic cycle (Scheme 6.8).7... 

An interesting reaction between the bis phenyl iodonium triflate of acetylene and the silyl enol ether of acetophenone afforded an allene (PhCOCH=C=C=CHCOPh, 84%) [6], Also, alkynyl iodonium tosylates and carbon monoxide in methanol or ethanol, with palladium catalysis, furnished alkyne carboxylates [53]. 

Muratake et al. reported the intramolecular a-arylation of ketones [55,56]. Thus, polycyclic compounds are readily obtained from aromatic keto-bromides and keto-triflates (Eq. 16). Bromo-amides can give the corresponding cycliza-tion products (Eq. 17) [52]. Related intramolecular vinylation reactions to give aliphatic polycyclic compounds have also been reported (Eq. 18) [57,581. The intramolecular cyclization of aromatic halo-ketones under carbon monoxide, which proceeds by mechanism C, gives the corresponding a-acylated products (Eq.l9) [321. 

This coupling when carried out in the presence of carbon monoxide (15-50 psi) results in cross-coupled ketones in generally good yield." This reaction is a particularly attractive route to divinyl ketones, which are substrates for Nazarov cyclization. The geometry of the vinyl triflate is retained. 

Reactions catalyzed by transition-metal complexes allow the synthesis of a variety of esters ruthenium(II) promotes the addition of acids to alkynes,379 380 e.g. 2,6-difluorobenzoic acid (9) undergoes addition to but-l-en-3-yne to furnish the enol ester 10.380 Aryl bromides381 and aryl or vinyl triflates,382-384 but also aryl chlorides when their tricarbonylchromium(O) complexes are used,385 react with palladium382- 385 or cobalt complexes38 to form a C —M bond. Insertion of carbon monoxide into the carbon-metal bond followed by trapping with an alcohol or phenol leads to ester formation, e.g. triflate 11 gives ester 12.382... 

In the Heck reaction, aryl, heterocyclic and vinyl halides - " or aryl triflates react with excess carbon monoxide and primary or secondary amines to give substituted amides, in the presence of a palla-dium(II) catalyst (equation 41). Cis- and trans-vinyl halides react stereoselectively. 

A more versatile palladium-catalyzed formylation of organic halides takes place using tributyltin hydride and carbon monoxide (equation 7). The reaction works for a variety of substrates — aryl, benzyl and vinyl iodides, vinyl triflates and allyl halides. Reaction conditions are mild (1-3 bar CO, 50 °C), and a variety of functional groups can be tolerated. With unsymmetrical allyl halides formylation is regio-selective, taking place at the less-substituted allylic position with retention of geometry at the allylic double bond. 

The reactions of allyl, alkenyl, and arylstannanes with allyl, alkenyl, and aryl halides or triflates proceed in the presence of palladium catalysts to give the cross-coupling products (eq (107)) [102]. In the reaction of alkenylstannanes, their configuration is generally retained. If these reactions are carried out in an atmosphere of carbon monoxide, the corresponding ketones are obtained (eq (108)) [103]. 

The anions generated from tetracarbonyl(phosphine) carbene complexes are more reactive in their reactions with organic electrophiles. This is consistent with the observation that the pATa of the methyl pentacarbonyl complex (88a) is increased by six orders of magnitude when one of the carbon monoxide ligands is replaced with tributylphosphine. The anion generated from (106) will give good yields of alkylated products with simple alkyl halides such as ethyl bromide however, dialkylation is still a serious side reaction. It has been reported that both pentacarbonyl and tetracarbonyl(phosphine) complexes can be efficiently monoalkylated with alkyl triflates (primary and secondary). The anion (89) for example, can be monoalkyated with the 3-butenyl triflate in 80% yield. ... 

Almost the same procedure except for using tributyltin hydride as the hydrogen source provides a convenient and versatile method for the synthesis of aldehydes from aryl iodides/bromides, benzylic and vinylic halides, vinylic triflates, and allylic halides. This protocol allows the reactions to proceed at ca. 50° and 1-3 atm of carbon monoxide, and a variety of functional groups can be tolerated (Eqs. 62-64). ... 

Following our first report on the palladium-catalyzed reaction of vinyl triflates with olefins (Heck-type reaction), oxidative insertion of palladium(O) into the carbon-oxygen bond of easily available vinyl triflates has proved to be a general method for the generation of o-vinyl palladium intermediates which can react directly with a variety of olefinic systems, carbon monoxide and alcohols or amines,or 1-alkynes, to give conjugated... 

---