Alkyl triflate

Use of mild conditions was crucial and the development of diimide reduction of singlet oxygenates, silver-salt-assisted displacement of halide by peroxide nucleophiles, peroxymercuration and demercuration, peroxide transfer from organotin to alkyl triflates, and oxygen trapping of azoalkane-derived diradicals have all played a part in providing the rich harvest of new bicyclic peroxides described herein. 

Alkyl trifluoromethanesulfonates — called alkyl triflates — react extremely rapidly in nucleophilic substitution reactions. 

The alkylation reaction is initiated by the activation of the alkene. With liquid acids, the alkene forms the corresponding ester. This reaction follows Markovnikov s rule, so that the acid is added to the most highly substituted carbon atom. With H2S04, mono- and di-alkyl sulfates are produced, and with HF alkyl fluorides are produced. Triflic acid (CF3S020H) behaves in the same way and forms alkyl triflates (24). These esters are stable at low temperatures and low acid/hydrocarbon ratios. With a large excess of acid, the esters may also be stabilized in the form of free carbenium ions and anions (Reaction (1)). 

Intermolecular reactions of hydroxylamines with secondary alkyl halides and mesylates proceed slower than with alkyl triflates and may not provide sufficiently good yield and/or stereoselectivity. A nseful alternative for these reactions is application of more reactive anions of 0-alkylhydroxamic acids or 0-alkoxysulfonamides ° like 12 (equation 8) as nucleophiles. The resulting Af,0-disubstituted hydroxamic acids or their sulfamide analogs of type 13 can be readily hydrolyzed to the corresponding hydroxylamines. The same strategy is also helpful for synthesis of hydroxylamines from sterically hindered triflates and from chiral alcohols (e.g. 14) through a Mitsunobu reaction (equation 9). 

A new method for synthesis of dialkyl peroxides is based on the novel peroxide transfer reaction between Ge or Sn peroxides and alkyl triflates. Mixed diaUcyl peroxides are obtained from the reaction of bis(butyltin)germyl peroxide with alkyl triflates. 

BusSnOOSnBus reacts with alkyl triflates to give symmetrical dialkyl peroxides, and with alkyl bistriflates to give 5-8 membered cyclic peroxides" , but no dialkyl peroxide is produced from f-butylperoxytrimethylsilane. Similarly, symmetrical dialkyl peroxides... 

HSAB is particularly useful for assessing the reactivity of ambident nucleophiles or electrophiles, and numerous examples of chemoselective reactions given throughout this book can be explained with the HSAB principle. Hard electrophiles, for example alkyl triflates, alkyl sulfates, trialkyloxonium salts, electron-poor car-benes, or the intermediate alkoxyphosphonium salts formed from alcohols during the Mitsunobu reaction, tend to alkylate ambident nucleophiles at the hardest atom. Amides, enolates, or phenolates, for example, will often be alkylated at oxygen by hard electrophiles whereas softer electrophiles, such as alkyl iodides or electron-poor alkenes, will preferentially attack amides at nitrogen and enolates at carbon. 

Lithiation and alkylation of the doubly allylic ether 23 with alkyl halides provides a useful synthesis of 1,3-butadienes. Alkyl triflates and tosylates, and carbonyl electrophiles, react with a-selectivity and give skipped dienes 24.23... 

The difluorovinyllithium 566 was initially prepared by in situ dehydrofluorina-tion-deprotonation of the TV.TV-diethyl carbamate derivative 568 with two equiv of LiTMP845 or LDA844,845 (Scheme 154). This intermediate 566 showed lower reactivity than the corresponding defluorinated system 561. Moderate to good yields were obtained with silicon, selenium and tin halides (38-80%)844,845,847 and alkyl triflates (71-91%)845, moderate reactivity being showed toward carbon dioxide and carbonyl compounds844,845,847. The reaction of intermediate 566 with aldehydes gave compound... 

Bates and Taylor reported the dialkylation of ketone o a -chanions using alkyl triflates (Table 6)30. Reactions of the dianions with methyl and ethyl triflates gave usee -alkylated... 

The preparation of alkoxy(l-alkynyl)carbene complexes (e.g., of compounds L M = C(OR1)—C=CR) mostly follows the two-step Fischer procedure,14 involving addition of a 1-lithio alkyne LiC=CR to a metal carbonyl L M(CO) to give a metal acylate L M=C(CTLi+) — C= CR14, which is subsequently alkylated with an oxonium salt [R130]BF4,15 an alkyl triflate R10S02C — CF3,16,22 or an alkyl fluorosulfonate R103SF16a,n ... 

Alkyl triflates are strong alkylation reagents and are able to alkylate phosphiranes and phosphirenes, respectively, to form phosphiranium or phosphirenium triflates examples are shown in Equation (8) <1997JOM(529)189> and Equation (9) <1998S175>. 

Reaction of Sulfonyl-Stabilized Oxiranyllitbiums. Reaction of sulfonyl-stabilized oxiranyllitbiums with primary alkyl halides gives acceptable yields of products. More reactive alkyl triflates give generally better yields but, due to the instability of oxiranyl-lithiums, yields are often not reproducible when electrophiles are added to a solution of the preformed oxiranyllitbiums. It is recommended that the alkylation reaction be carried out by an in situ trapping method. Treatment of a solution of epoxy sulfone (1.0 equiv) and triflate (1.5 equiv) in THE-DMPU (or HMPA) at — 100 °C under argon with n-BuLi (1.0 equiv) followed by stirring... 

While alkylation of sulfonyl-stabilized oxiranyllithiums with primary alkyl triflates proceeds in high yield, the reaction towards epoxides is relatively slow ( 2 h) and the decomposition of oxiranyllithium is marked, such that it decreases the yield, especially in the case of a Z-isomer (eq 7 and 8). Addition of boron trifluoride diethyl etherate promotes this epoxide-epoxide coupling reaction. One of the diastereoisomers of eq 8 has been elaborated via 5-endo cyclization into a marine tetrahydrofuran isolated from a brown alga. ... 

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