Vinyl triflates carbonylation

Palladium complexes also catalyze the carbonylation of halides. Aryl (see 13-13), vinylic, benzylic, and allylic halides (especially iodides) can be converted to carboxylic esters with CO, an alcohol or alkoxide, and a palladium complex. Similar reactivity was reported with vinyl triflates. Use of an amine instead of the alcohol or alkoxide leads to an amide. Reaction with an amine, AJBN, CO, and a tetraalkyltin catalyst also leads to an amide. Similar reaction with an alcohol, under Xe irradiation, leads to the ester. Benzylic and allylic halides were converted to carboxylic acids electrocatalytically, with CO and a cobalt imine complex. Vinylic halides were similarly converted with CO and nickel cyanide, under phase-transfer conditions. ... 

Recent contributions from Vogel s group have shown that, under CO atmosphere and in the presence of Pd2(dba)3 and Ph3As, 1-stannyl glycals can be carbonylated and coupled to organic halides (Scheme 6a),38 or vinyl triflates (Scheme 6b),39 in carbonylative Stifle cross-coupling processes.40 Also of interest is the palladium catalyzed cross-coupling reaction of... 

Alkyl halides possessing / -hydrogens are usually poor substrates for carbonylative cross-coupling due to competitive / -hydride elimination/ Allyl chlorides can be used in carbonylative cross-coupling with allylstannanes/ phenyl-, 3-furyl, or vinylstannanes " to afford allylketones in modest to good yields. Divinylketones can be accessed through the reaction of vinylstannanes with vinyl iodides or vinyl triflates, with the latter requiring the addition of LiCl. Synthetic potential of this method has been proved in the formation of macrocyclic ketone jatrophone. In the reaction of vinyl triflates with tetramethyltin or aryltrimethylstannanes the additional activation by ZnCle is required. 

Carbonylative coupling of vinyl triflates with organotins (12, 470-471).3 The final step in a synthesis of the macrocyclic diterpene jatrophone (2) was effected by carbonylative coupling of a vinyl triflate with vinyltin catalyzed by bis(acetonitrile)-dichloropalladium. 

Vinyl triflates (10, 123).1 The most satisfactory conditions for preparation of vinyl triflates from carbonyl compounds using triflic anhydride and catalyzed by the pyridine 1 or the polymer-bound reagent 2 are discussed by Wright and Pulley. In the case of aldehydes, the reaction is best carried out in CHC13 or (CH2C1)2 at 50-70°, and results in a gem-bistriflate, which decomposes thermally to the vinyl triflate. These conditions, when applied to a ketone, particularly aldol-prone ones, are usually not useful. The preferred solvent is nonpolar (CClt) with a reaction temperature of about 50°. In addition, the Tf20 should be freshly distilled from P205. 

Scheme 4 gives the endgame from Corey s cyclization product 4 (Scheme 1) to the marine natural product scalarenedial (20, [15]), which is a strong fish feeding deterrent. The Barton-McCombie process [16] was employed to deoxygenate at C3, followed by conversion of the ketone to the vinyl triflate 18 with PhNTf2 (McMurry s method [17]). After hydroxy-desilylation of 18, the carbonylation to 19 was catalyzed by Pd(dppp) (see above). The vicinal... 

Two new reports have provided examples of the potential utility of indol-2-ylborates for elaboration of indoles. Pd-Catalyzed carbonylation with vinyl triflates was used to prepare 2-(cyclohex-1 -enoyl)indoles which were then converted to yuehcukene analogs. <95H(41) 1385>... 

Fig (22) 2-isopropylphenol (183) is converted to allylic alcohol (185). Its bromide derivative reacts with methyl acetoacetate. The resulting compound undergoes radical cyclization yields ketoester (186) whose vinyl triflate on reduction and carbonylation furnishes lactone (187). Diol (188) obtained from (187), is converted to monoepoxide (189) which on further epoxidation produces triptonide (148). Its conversion to triptolide (149) is accomplished by reduction. 

Blaser and Spencer used aroyl halides in place of aryl halides, with aroyl chlorides being of specific interest as ubiquitous, relatively cheap compounds ( Blaser reaction ) [24], This latter reaction is normally conducted in aromatic solvents phosphines are not used here as catalyst ligands since they fully inhibit the reaction. In the same way, benzoic acid anhydrides can be used as the aryl source in combination with PdCl2 and catalytic amounts of NaBr [79]. In this reaction, one of the arenes is used in the coupling reaction by elimination of CO, whereas the other benzoate serves as the base. The benzoic acid thus formed can easily be recycled into the anhydride. The use of aryl and vinyl triflates according to Cacchi [25] and Stille [26] extends the scope of the Heck coupling to carbonyl compounds phenol derivatives act via triflate functionalization as synthetic equivalents of the aryl halides. The arylation of cyclic alkenes [27], electron-rich vinyl ethers [28], and allylic alcohols [29] is accessible through Heck reactions. Allylic alcohols yield C-C-saturated carbonyl compounds (aldehydes) for mechanistic reasons (y9-H elimination), as exemplified in eq. (6). 

Gyorkos, A. C., Stille, J. K., Hegedus, L. S. The total synthesis of ( )-epi-jatrophone and ( )-jatrophone using palladium-catalyzed carbonylative coupling of vinyl triflates with vinyl stannanes as the macrocycle-forming step. J. Am. Chem. Soc. 1990,112, 8465-8472. 

In the borylation of vinyl triflates (3-substituted by a carbonyl group, use of potassium carbonate (K2CO3) (207mg, 1.5 mmol) in dry 1,4-dioxane (4mL) at 80 °C gives better results. 

Procedures for Pd-catalyzed coupling with carbonylation to give 2-acyl indoles were also reported. Triethyl(l-methylindol-2-yl)borate, which can be prepared from 1-methylindole by lithiation followed by addition to triethylborane, was coupled with aryl iodides and vinyl triflates to give 2-acyl indoles in 20-80% yield. <94J0C2634> The reactions were run with PdClj(PPh3)2 as catalyst under 15 atm of CO at 90 . 

Vinyl triflates serve as substrates for Pd(Ph3P)4-catalyzed carbonylation and have been converted into the corresponding esters or ketones (eq 23). 

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