Allyl triflates

Trifluoromethanesulfonate esters ( triflates ) of allyl alcohol and its derivatives are very reactive and undiluted samples must be stored in vented containers at — 78° C. A chilled sample of allyl triflate in a sealed ampoule exploded on being allowed to warm to ambient temperature. The esters react violently with aprotic solvents such as DMF or DMSO. Individually indexed compounds are ... 

Allyl triflate, CHa CHCHaOSOaCFa (1). Mol. wt. 191.16, colorless liquid, must be stored at —78° in a vented flask. This triflate can be prepared in pure form in 69yo yield by the reaction of allyl alcohol with trifluoromethanesulfonic anhydride and pyridine in dichloromethane. ... 

Ring expansion. Vedejs and Schmid have devised a repeatable ring expansion process involving successive [2,3]sigmatropic shifts as illustrated in scheme (I). An -vinyl heterocycle such as 2-vinylthiacyclopentane (2) is alkylated with allyl triflate to give the salt 3. On treatment with a base (DBU) in acetonitrile,... 

RING EXPANSION Allyl triflate. Chromium carbonyl. Ethyl diazOacetate. Thallium(III) nitrate. 

Further lithiation of 111 followed by reaction with allyl triflate as the electrophile provided highly enantioenriched benzylamines 112 with quaternary centers [82]. The enantiomer of 112 can be prepared from 113 by a similar reaction sequence (Scheme 33). 

Haseltine has described an enantioselective formal synthesis of pancratistatin in which the stereocontrol is driven by the aeetonide of conduritol A. The enantioselective hydrolysis (desymmetrization) of this compound was achieved with a lipase, and the aryl-cyclohexane ring bond was formed through an intramolecular cyclization of the activated benzene ring with an allylic triflate (278). Plumet reported a total synthesis of (-l-)-7-deoxypaneratistatin based on the conjugate addition of an aryl-lithium species to a bicyclic conjugated sulfone derived from furan, which enabled the efficient installation of the six stereogenic centers of the cyclohexane ring (279) (Scheme 13). 

As demonstrated below, the general procedure begins by treatment of camphor with triflic anhydride and a non-nucleophilc base to give allyl triflate 107 via Wagner-Meerwein rearrangement of 105 followed by elimination. Reduction of 107 with LiAULj then results in allylic alcohol... 

The asymmetric deprotonation of carbamates can be extended beyond pyrrolidines. Beak, for example, disclosed metalation of benzylamine 60 and alkylation of the resulting carbanion with methyl triflate to furnish 61 in 98 % ee (Scheme 13.10) [55]. Subsequent proton abstraction from 61 was effected with u-BuLi in the presence of TMEDA, followed by stereospecific alkylation with allyl triflate. Following removal of the p-methoxybenzyl group (CAN), the trisubstituted carbamate 62 was isolated in 97 % ee. 

Allylic amines are coupled to halides giving either allylic amines or enamines depending on the reaction condition. Reaction of steroidal dienyl triflate with Boc-diprotected allylamine affords allylamine. Use of AcOK as a base is crucial for the clean coupling[102]. The tert-allylic amine 123 reacts with an aryl halide to give the enamine 125 in DMF and allylic amine 124 in nonpolar solvents[103]. 

The alkenyloxirane 126 in excess reacts with aryl and alkenyl halides or triflates in the presence of sodium formate to afford the allylic alcohol 127[104], Similarly, the reaction of the alkenyloxetane 128 gives the homo-allylic alcohol 130[105]. These reactions can be explained by insertion of the double bond in the Ar—Pd bond, followed by ring opening (or /3-eliraination) to form the allylic or homoallylic alkoxypalladium 129, which is converted into the allylic 127 or homoallylic alcohol 130 by the reaction of formate. The 3-alkenamide 132 was obtained by the reaction of the 4-alkenyl-2-azetizinone 131 with aryl iodide and sodium formate [106]. 

Allenes also react with aryl and alkenyl halides, or triflates, and the 7r-allyl-palladium intermediates are trapped with carbon nucleophiles. The formation of 283 with malonate is an example[186]. The steroid skeleton 287 has been constructed by two-step reactions of allene with the enol trillate 284, followed by trapping with 2-methyl-l,3-cyclopentanedione (285) to give 286[187]. The inter- and intramolecular reactions of dimethyl 2,3-butenylmalonate (288) with iodobenzene afford the 3-cyclopentenedicarboxylate 289 as a main product) 188]. 

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]. 

Aryl halides react with a wide variety of aryl-, alkenyl- and alkylstan-nanes[548-550]. Coupling of an aryl tritlate with an arylstannane is a good preparative method for diaryls such as 688. The coupling of alkenylstannanes with alkenyl halides proceeds stereospecifically to give conjugated dienes 689. The allylstannane 690 is used for allylation[397,546,551-553]. Aryl and enol triflates react with organostannanes smoothly in the presence of LiCl[554]. 

CoupDng of ongarxjtin reagents (and Pd catalyst) with aryl or vinyl haiidas or triflates, acyl chlorides or allyl acetates. 

Benzyl and allyl alcohols which can generate stabilized caibocations give Friedel-Crafts alkylation products with mild Lewis acid catalysts such as scandium triflate. ... 

The oxidative dimerization of the anion of methyl phenyl sulfone (from a Grignard reagent) in ethereal solution in the presence of cupric chloride in 5% yield has been reported47. Despite the reported48 poor stability of the a-sulfonyl C-centered radicals, Julia and coworkers49 provoked the dimerization (in 13 to 56% yields) of the lithiated carbanion of alkyl phenyl sulfones using cupric salts as oxidants. The best results are obtained with cupric triflates in THF-isobutyronitrile medium (56% yield for R = H). For allyl phenyl sulfones the coupling in the 3-3 mode is predominant. 

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. ... 

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