TMSOTf Research Articles

Diastereoselective Synthesis of Dihydropyrans via Prins Cyclization of Enol Ethers: Total Asymmetric Synthesis of (+)-Civet Cat Compound

Trimethylsilyl trifluoromethanesulfonate (TMSOTf) can be efficiently used for Prins cyclization of acrylyl enol ethers to 5,6-dihydro-2H-pyran-2-acetates stereo- and regioselectively in good yields. The methodology was used for the total synthesis of natural product (+)-civet.

Regioselective Synthesis of Trichloromethyl‐Substituted Salicylates and Cyclohexenones by One‐Pot Cyclizations of 1,3‐Bis(trimethylsilyloxy)buta‐1,3‐dienes

AbstractA variety of 6‐(trichloromethyl)salicylates (=2‐hydroxy‐6‐(trichloromethyl)benzoates) were prepared by TiCl4‐mediated cyclization of 1,3‐bis(trimethylsilyloxy)buta‐1,3‐dienes with 1,1,1‐trichloro‐4,4‐dimethoxybut‐3‐en‐2‐one. The employment of trimethylsilyl trifluoromethanesulfonate (Me3SiOTf) as Lewis acid resulted in the formation of trichloromethyl‐substituted cyclohexenones. The cyclizations proceeded with good‐to‐very‐good regioselectivities.

A Lewis acid-promoted Pinner reaction

Carbonitriles and alcohols react in a Lewis acid-promoted Pinner reaction to carboxylic esters. Best results are obtained with two equivalents of trimethylsilyl triflate as Lewis acid. Good yields are achieved with primary alcohols and aliphatic or benzylic carbonitriles, but the straightforward synthesis of acrylates and benzoates starting with acrylonitrile and benzonitrile, respectively, is similarly possible. Phenols are not acylated under these reaction conditions. The method has been used for the first total synthesis of the natural product monaspilosin. In the reaction of benzyl alcohols variable amounts of amides are formed in a Ritter-type side reaction.

One‐Pot Enol Silane Formation/Mukaiyama–Mannich Addition of Ketones, Amides, and Thioesters to Nitrones in the Presence of Trialkylsilyl Trifluoromethanesulfonates

AbstractKetones, amides, and thioesters form enol silanes and add to N‐phenylnitrones in one pot in the presence of trimethylsilyl trifluoromethanesulfonate and trialkylamine. The reaction is general to a range of silyl trifluoromethanesulfonates and N‐phenylnitrones. The β‐(silyloxy)amino carbonyl products are stable to chromatography and can be isolated in 63–99 % yield.

Synthesis and Reactivity of the New Trimethylsilyl Esters of Aminomethylenebisorganophosphorus Acids

ABSTRACTThe interaction of trimethylsilyl esters of trivalent organophosphorus acids containing PH and POSiMe3 fragments in the presence of trimethylsilyl trifluoromethanesulfonate as catalyst is proposed as a convenient method for the synthesis of new trimethylsilyl esters of aminomethylenebisorganophosphorus acids with three and four coordinated phosphorus. Also the new functionalized derivatives of the aminomethylenebisphosphinic acids with substituted hydroxymethyl moieties are synthesized, and some properties of the obtained compounds are presented.

Synthesis of N-substituted aminomethylenediphosphonites and their derivatives

Substituted aminomethylenediphosphonites are of interest as the key materials in the synthesis of functionalized aminomethylenediphosphorus-containing compounds, which are analogs of natural organophosphorus pyrophosphates and amino acids, promising ligands and biologically active substances with diverse properties [1]. Recently, we have prepared two types of the compounds by reacting bis(trimethylsiloxy) phosphine with substituted methyleneimines [2]. To synthesize new types of N-substituted aminomethylenediphosphonites we studied the direct interaction of bis(trimethylsiloxy) phosphine A with available Nsubstituted formamides. Note that the phosphine A can be easily attached to the carbonyl groups of various aldehydes and ketones [3], but the analogous reaction with formamide is not described. The reaction of an excess of bis(trimethylsiloxy)phosphine A with Nsubstituted formamides proceeds readily in methylene chloride only in the presence of a catalyst (trimethylsilyl trifluoromethanesulfonate) to give the intermediate diphosphonites B. The latter react with bis(trimethylsilyl)amine under reflux in the presence of trimethylchlorosilane to afford diphosphonites I–III with good yields (cf. [4]). DOI: 10.1134/S1070363213060340

Stereocontrolled Total Synthesis of Polygalolide A

The total synthesis of polygalolide A, a secondary metabolite that was isolated from a Chinese medicinal plant, is reported. A key issue in this synthesis was construction of an oxabicyclo[3.2.1] skeleton, which was solved by the development of an intramolecular Ferrier-type C-glycosylation of a glucal with siloxyfuran as an internal nucleophile. The substrate was prepared from D-glucal by the introduction of trimethylsilylacetylene and siloxyfuran groups. Although C-glycosylation did not occur under the conditions found from model experiments, further examination revealed that the combination of trimethylsilyl trifluoromethanesulfonate (TMSOTf) and 2,4,6-collidine successfully afforded the desired product as a single diastereomer. The siloxy group at the C3 position played a crucial role in the stereocontrol of this reaction. The product was further transformed into a tetracyclic compound as follows: The vinyl ether and acetylenic moieties were reduced and the siloxy group was removed with a Barton-McCombie reaction. The construction of the six-membered ether and the γ-lactone provided the tetracyclic compound. Finally, a phenolic moiety was introduced by using a Mukaiyama aldol reaction to furnish polygalolide A.

Mechanism of the Pummerer Reaction: A Computational Study

DFT calculations are used to investigate the mechanism of the Pummerer reaction between a chiral sulfoxide and acetic anhydride under classical and stereoselective reaction conditions (without and with additives, respectively). The first step involving acetylation of the sulfoxide with release of acetate is found to be rate-determining in both cases. For the stereoselective Pummerer reaction in the presence of trimethylsilyl triflate (TMSOTf) and N,N-dimethylacetamide (DMAC), TMSOTf- and DMAC-assisted transition states as well as ion exchange reactions are considered to account for the role of TMSOTf and DMAC.

Subtle Electronic Effects in Metal-Free Rearrangement of Allenic Alcohols

A general and stereoselective rearrangement of allenic alcohols to (E,E)-1,3-dien-2-yl triflates and chlorides was developed under metal-free conditions. Subtle electronic effects of the alkyl and aryl substituents on the carbon bearing the hydroxyl group has a profound impact on the reaction rate and efficiency such that vinyl triflates were obtained from electron-deficient substrates and trimethylsilyl triflate whereas vinyl chlorides were generated with an electron-rich substrate and trimethylsilyl chloride.

Lewis Acid Catalyzed Enlargement of Cyclic β‐Alkoxyenals and One‐Pot Synthesis of Polyfunctional Enoxysilanes Derived from Aucubin with Trimethylsilyldiazomethane

Pyrane to oxepane in one step: Highly regio- and stereoselective homologations dependent on the nature of carbonyl function and catalysts have been observed during the formation of enoxysilanes (see scheme). Trimethylsilyl trifluoromethanesulfonate (TMSOTf) and AlCl3 were identified as suitable catalysts to promote the homologation and ring-enlargement.

A new synthetic approach to elvucitabine

A new synthetic approach to elvucitabine started from L-xylose via the reactions of 10 steps in an overall yield of 20% was developed. The key steps included trimethylsilyl trifluoromethanesulfonate(TMSOTf)-mediated stereocontrolled β-glycosidation and exquisite choice of chloroacetyl group for the protection of hydroxyl groups as well as the corresponding deprotection under notably mild conditions. The structure of elvucitabine, in particular, the stereochemistry thereof, was unambiguously determined by comparison of the physical properties, such as 1H NMR data and the specific rotation, of the synthesized sample with those reported.

3-Bromopenta-2,4-dienylsilane: a useful reagent for the preparation of [3]dendralenes and polycyclic compounds

Starting from (Z)-1-trimethylsilyl-3-bromopenta-2,4-diene, a lithium-bromine exchange reaction followed by addition onto carbonyl compounds provided the corresponding dienyl alcohols. A Peterson-type γ-elimination promoted by a catalytic amount of trimethylsilyl triflate cross-conjugated gave triene systems ([3]dendralene) which rapidly reacted with the appropriate dienophiles to yield tandem intermolecular Diels-Alder cycloadducts.

Methodology for <i>in Situ</i> Protection of Aldehydes and Ketones Using Trimethylsilyl Trifluoromethanesulfonate and Phosphines: Selective Alkylation and Reduction of Ketones, Esters, Amides, and Nitriles

A methodology for selective transformations of ketones, esters, Weinreb amides, and nitriles in the presence of aldehydes has been developed. The use of a combination of PPh(3)-trimethylsilyl trifluoromethanesulfonate (TMSOTf) promotes selective transformation of aldehydes to their corresponding, temporarily protected, O,P-acetal type phosphonium salts. Because, hydrolytic work-up following ensuing reactions of other carbonyl moieties in the substrates liberates the aldehyde moiety, a sequence involving aldehyde protection, transformation of other carbonyl groups, and deprotection can be accomplished in a one-pot manner. Furthermore, the use of PEt(3) instead of PPh(3) enables ketones to be converted in situ to their corresponding O,P-ketal type phosphonium salts and, consequently, selective transformations of esters, Weinreb amides, and nitriles in the presence of ketones can be performed. This methodology is applicable to various dicarbonyl compounds, including substrates that possess heteroaromatic skeletons and hydroxyl protecting groups.

Efficient α-Mannosylation of Phenols: The Role of Carbamates as Scavengers for Activated Glycosyl Donors

The boron trifluoride activation of trichloroacetimidate donors was found to be an efficient method for the α-mannosylation of tyrosine-containing acceptors. Most notably, these conditions are compatible with the commonly used carbamate protecting groups, whereas trichloroacetimidate activation with trimethylsilyl triflate or the use of glycosyl sulfoxides led to diminished yields in the presence of carbamates. In these cases, the competing reaction of the activated donors with the carbamate group was identified as a problematic side reaction. Taking advantage of this reactivity, various glycosyl carbamates were generated for the first time under non-acidic glycosylation conditions by reaction of different Boc-protected amino acids and dipeptides with glycosyl sulfoxides under triflic anhydride activation.

Novel Synthesis of 4,5-Unsubstituted 2,3-Dihydroisoxazoles from 5-Acetoxyisoxazolidines

A new synthetic method for the preparation of 4,5-unsubstituted 2,3-dihydroisoxazoles from readily available 5-acetoxyisoxazolidines is presented. Elimination reactions are carried out in anhydrous N-methylpyrrolidin-2-one (NMP) with a catalytic amount of trimethylsilyl triflate in the presence of N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) and provide the 2,3-dihydroisoxazoles in very good yields. The nature of the silylating agent plays a very important role in elimination process. Anhydrous reaction conditions are required, while trimethylsilanol, the product of trimethylsilyl triflate and N,O-bis(trimethylsilyl)trifluoroacetamide hydrolysis, can initiate reactions leading to deacetylation, giving side products and thus decreasing the total yield of the elimination.

Acid-mediated coupling of γ-hydroxybutenolides and aldehydes: synthesis of a new class of spirocyclic ketal-lactones

In the presence of trimethylsilyl trifluoromethanesulfonate (TMSOTf), γ-methyl-γ-hydroxybutenolide reacts with aromatic aldehydes to generate a new class of stereochemically rich spirocyclic ketal-lactones in good yields and with excellent stereoselectivities. We believe that this process takes place through the in situ generation of protoanemonin followed by a Prins reaction. Herein, we describe this discovery, along with substrate scope and preliminary mechanistic studies.

A Hydrogen Chloride‐Free Pinner Reaction Promoted by Lewis Acids

AbstractA hydrogen chloride‐free variation of the Pinner reaction was developed, in which alcohols react with carbonitriles to furnish carboxylates. Best results were achieved with aliphatic alcohols, and aliphatic or benzylic nitriles in the presence of 2 equiv. of trimethylsilyl triflate (Me3SiOTf). With these substrates, yields exceeding 80% were achieved. A strictly neutral variation of this protocol is possible, when 1 equiv. of Et3N is added to the reaction mixture.

Synthesis and Absolute Configuration of the 7-Phenylhepta-4,6-diyne-1,2-diol Isolated from Bidens pilosa

Correction to: Synthesis and Absolute Configuration of the 7-Phenylhepta-4,6-diyne-1,2-diol Isolated from Bidens pilosaSynthesis 2011; 2011(13): 2131-2135DOI: 10.1055/s-0030-1260604

An improved strategy for the synthesis of [¹⁸F]-labeled arabinofuranosyl nucleosides.

The expression of the herpes simplex virus type-1 thymidine kinase (HSV1-tk) gene can be imaged efficaciously using a variety of 2'-[(18)F]fluoro-2'-deoxy-1-b-D-arabinofuranosyl-uracil derivatives [[(18)F]-FXAU, X=I(iodo), E(ethyl), and M(methyl)]. However, the application of these derivatives in clinical and translational studies has been impeded by their complicated and long syntheses (3-5h). To remedy these issues, in the study at hand we have investigated whether microwave or combined catalysts could facilitate the coupling reaction between sugar and nucleobase and, further, have probed the feasibility of establishing a novel approach for [(18)F]-FXAU synthesis. We have demonstrated that the rate of the trimethylsilyl trifluoromethanesulfonate (TMSOTf)-catalyzed coupling reaction between the 2-deoxy-sugar and uracil derivatives at 90 °C can be significantly accelerated by microwave-driven heating or by the addition of Lewis acid catalyst (SnCl(4)). Further, we have observed that the stability of the α- and β-anomers of [(18)F]-FXAU derivatives differs during the hydrolysis step. Using the microwave-driven heating approach, overall decay-corrected radiochemical yields of 19%-27% were achieved for [(18)F]-FXAU in 120min at a specific activity of >22MBq/nmol (595Ci/mmol). Ultimately, we believe that these high yielding syntheses of [(18)F]-FIAU, [(18)F]-FMAU and [(18)F]-FEAU will facilitate routine production for clinical applications.

A high-yielding synthesis of allyl glycosides from peracetylated glycosyl donors

β-Configured peracetylated sugars are often used as easily accessible glycosyl donors that are typically activated with common Lewis acids such as boron trifluoride or trimethylsilyltrifluoromethane sulfonate. Often these glycosylations occur with unsatisfactory yields due to incomplete reactions or extensive byproduct formation, primarily as a result of loss of an additional acetyl group generating partially unprotected glycosides. Here we report a simple glycosylation–reacetylation protocol for the generation of predominantly β-configured peracetylated allyl glucoside, -galactoside, -lactoside, and -maltoside with substantially improved reaction yields.