Carbonylation alkenyl triflates

Scheme 7.3 Heck reactions of Af-methoxy-carbonyl-2-pyrroline with aryl or alkenyl triflates with (it)-BITIANP.

The addition of LiCl and Cul, and triphenylarsine as ligand are required to suppress side-reactions in the carbonylative cross-coupling of geminally substituted alkenyl triflate in the synthesis of sarcodictyin. Stereochemical configuration of the double bond of organotin compound was completely lost in this reaction (Equation (5)). " ... 

The carbonylation of aryl iodide in the presence of terminal alkynes affords acyl alkynes. Bidentate ligands such as DPPF give good results [241]. When PI13P is used, phenylacetylene is mainly converted to diphenylacetylene. The alkynyl ketones 488 are prepared by the reaction of the alkenyl triflate 487 with phenylacetylene and CO [242],... 

The reactions have a very wide scope. Acyl halides serve as substrates for Stille couplings in addition to the usual aryl and alkenyl halides however, most alkyl halides cannot be used as substrates. Like Pd-catalyzed carbonylations, reactions proceed most quickly when X = I and rather slowly when X = Cl. Again, triflates are also widely used, especially alkenyl triflates, which are easily prepared from the ketones. The nucleophile may be C(sp), C(sp ), or C(sp ), and nucleophiles other than C nucleophiles (e.g., Me3Sn—SnMes and R2N— Na) may also be used. 

Aryl and alkenyl triflates prepared from phenols and carbonyl compounds are reactive substrates which undergo facile oxidative addition. Reactivity of triflates is between that of iodides and bromides. Pd-catalyzed reactions of triflates mean indirect displacement of the phenolic OH group to afford 80 and transformation of carbonyl compounds 81 to the substituted alkenes 82. In classical organic chem-... 

Aldehydes are prepared by carbonylation in the presence of hydride sources. Formation of aldehydes can be understood by transmetallation of acylpalladium 56 with a hydride to give acylpalladium hydride 57, followed by reductive elimination. Metal hydrides and hydrogen are used for aldehyde synthesis. Hydrosilane is one of the hydrides. Reaction of /I-naphthyl triflate (58) with EtsSiH using DPPF as a ligand under mild conditions afforded the aldehyde 59 [28]. Carbonylation of the alkenyl triflate 60 in the presence of tin hydride and LiCl afforded the aldehyde 61 in 95 % yield [29]. 

The same year, Hayashi and colleagues described an enantioselective palladium-catalyzed intramolecular carbonylative coupling of aryl and alkenyl triflates [29]. Enantiomerically enriched cyclopentenones were prepared in high yields... 

Scheme 7.10 Palladium-catalyzed intramolecular carbonylative coupling of aryl and alkenyl triflates to cyclopentenones...

The use of vinyl inflates in place of halides is attractive due to their easy formation from ketones and the readiness with which they undergo Pd-catalyzed chemistry. A method for the carbonylation of hydroxy alkenyl triflates using Pd(PPh3)4 as catalyst was developed by Crisp and Meyent ii A variety of fused butenolides were synthesized in good to excellent yields using this protocol, as shown in Scheme 9. 

Procedures for carbonylation of alkenyl triflates are also successful. 

Diene carboxylates can be prepared by the reaction of alkenyl halides with acrylates[34]. For example, pellitorine (30) is prepared by the reaction of I-heptenyl iodide (29) with an acrylate[35]. Enol triflates are reactive pseudo-halides derived from carbonyl compounds, and are utilized extensively for novel transformations. The 3,5-dien-3-ol triflate 31 derived from a 4,5-unsaturated 3-keto steroid is converted into the triene 32 by the reaction of methyl acrylate[36]. 

Aldehydes can also be prepared by the carbonylation of aryl and alkenyl halides and triflate, and benzyl and allyl chlorides using tin hydride as a hydride source and Pd(PhjP)4 as a catalyst[377]. Hydrosilancs arc used as another hydride source[378]. The arenediazonium tetralluoroborate 515 is converted into a benzaldehyde derivative rapidly in a good yield by using Et ,SiH or PH MS as the hydride source[379]. 

The reaction of alkenyl iodides or triflates, alkenylstannanes, and CO affords divinyl ketones[397,398]. Thus the capnellene skeleton 538 has been synthesized by the carbonylation of the cyclopentenyl triflate 536 with the alkenyltin 537[392], The macrocyclic divinyl ketone 540 has been prepared in a moderate yield by the carbonylative cyclization of 539[399]. 

Transition metal-catalyzed transformations are of major importance in synthetic organic chemistry [1], This reflects also the increasing number of domino processes starting with such a reaction. In particular, Pd-catalyzed domino transformations have seen an astounding development over the past years with the Heck reaction [2] - the Pd-catalyzed transformation of aryl halides or triflates as well as of alkenyl halides or triflates with alkenes or alkynes - being used most often. This has been combined with another Heck reaction or a cross-coupling reaction [3] such as Suzuki, Stille, and Sonogashira reactions. Moreover, several examples have been published with a Tsuji-Trost reaction [lb, 4], a carbonylation, a pericyclic or an aldol reaction as the second step. 

Alkenyl trifluoromethanesulphonates (enol triflates) undergo Heck coupling with alkenes efficiently (equation 123)209a 215. This reaction is a useful variation of the use of vinyl halides not only because they are easy to prepare from the corresponding carbonyl compounds, but also because yields are good, and the stereochemistry of the triflate is largely maintained. 

The substrates with the alkenyl iodide (138-141) moiety could be totally converted into the desired products (138a, 139a, 138b-140b, 138c-141c) in4-8 h, while the enol triflate (142) reacted slowly. The bromo derivative (144) is unreactive and no carbonylation product was observed even after prolonged reaction times. 

The carbonylation of the same substrates (138-144) with several A-substituted hydrox-ylamines proceeds with the same order of substrate reactivity (Scheme 67). In particular, with steroidal alkenyl iodides 138-141 and enol triflates 142 and 143 complete conversion of the substrates could be achieved, in the latter cases (142 and 143) with long reaction times. The analogue bromo derivative 144 is completely unreactive. 

Lithium triethyl(l-methylindolyl-2)borate has been introduced as a convenient source of indolyl residue for carbonylative cross-coupling with aryl iodides, alkenyl iodides, or triflates. The reaction requires elevated CO pressure and high loading of catalyst (5mol.%) (Equation (15)). Aryl and alkenyl bromides, as well as aryl iodides... 

The carbonylation of o-diiodobenzene with a primary amine affords the phthalimide 501 [355,356], Carbonylation of iodobenzene in the presence of odiaminobenzene (502) and DBU or 2,6-lutidine affords 2-phenylbenzimida-zole (503)[357], The carbonylation of aryl iodides in the presence of pentafluor-oaniline affords 2-arylbenzoxazoles directly. 2-Arylbenzoxazole is prepared indirectly by the carbonylation of n-aminophenol[358]. The optically active aryl or alkenyl oxazolinc 505 is prepared by the carbonylation of the aryl or enol triflates in the presence of the opticaly active amino alcohol 504, followed by treatment with thionyl chloride[359]. 

Alkenyl halides and their pseudohalides also react with Pd(0) to form the alkenylpalladium intermediates 11, and their transformations are summarized in Scheme 3.4. In addition to alkenyl halides, the enol triflates 12 undergo oxidative addition, showing that carbonyl compounds are useful starting compounds for Pd-catalysed reactions. 

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