Alkylation of thiols with trichloroacetimidates under neutral conditions

Alkylation of Isatins with Trichloroacetimidates

N-Alkylation of isatins can be achieved utilizing trichloroacetimidate electrophiles and a Lewis acid catalyst. These reactions provide access to N-alkyl isatins, versatile scaffolds which are often employed in the synthesis...

Selective C-H chalcogenation of thiazoles via thiazol-2-yl-phosphonium salts

Thiazoles and benzothiazoles undergo regioselective C2-H chalcogenation via the sequence of thiazole C2-functionalization with phosphines to produce phosphonium salts which in turn react with S- and Se-centered nucleophiles to give products of C2-H chalcogenation and allow for recovery of the starting phosphine. The atom economical sequence proceeds under mild conditions and features broad scope for both the nucleophiles (electron-rich, electron-poor, sterically hindered thiols) and the various substituted benzothiazoles. The access to the substituted medicinally relevant C2-thio benzothiazoles also enables stereoselectivity improvements in the modified Julia olefinations.

Esterifications with 2-(Trimethylsilyl)ethyl 2,2,2-Trichloroacetimidate

2-(Trimethylsilyl)ethyl 2,2,2-trichloroacetimidate is readily synthesized from 2-trimethylsilylethanol in high yield. This imidate is an effective reagent for the formation of 2-trimethylsilylethyl esters without the need for an exogenous promoter or catalyst, as the carboxylic acid substrate is acidic enough to promote ester formation without an additive. A deuterium labeling study indicated that a β-silyl carbocation intermediate is involved in the transformation.

Dialkylation of Indoles with Trichloroacetimidates to Access 3,3-Disubstituted Indolenines

2-Substituted indoles may be directly transformed to 3,3-dialkyl indolenines with trichloroacetimidate electrophiles and the Lewis acid TMSOTf. These reactions provide rapid access to complex indolenines which are present in a variety of complex natural products and medicinally relevant small molecule structures. This method provides an alternative to the use of transition metal catalysis. The indolenines are readily transformed into spiroindoline systems which are privileged scaffolds in medicinal chemistry.

Promoting Effect of Crystal Water Leading to Catalyst-Free Synthesis of Heteroaryl Thioether from Heteroaryl Chloride, Sodium Thiosulfate Pentahydrate, and Alcohol

It is observed the crystal water in sodium thiosulfate pentahydrate (Na₂S₂O₃·5H₂O) can promote its multicomponent reaction with heteroaryl chlorides and alcohols, providing a facile, green, and specific synthesis of unsymmetrical heteroaryl thioethers via one-step formation of two C-S bonds under catalyst-, additive-, and solvent-free conditions. Mechanistic studies suggest that the crystal water in Na₂S₂O₃·5H₂O is crucial in generating the key thiol intermediates and byproduct NaHSO₄, which then catalyzes the dehydrative substitution of alcohols with thiols to afford thioethers.

Ester Formation via Symbiotic Activation Utilizing Trichloroacetimidate Electrophiles

Trichloroacetimidates are useful reagents for the synthesis of esters under mild conditions that do not require an exogenous promoter. These conditions avoid the undesired decomposition of substrates with sensitive functional groups that are often observed with the use of strong Lewis or Brønsted acids. With heating, these reactions have been extended to benzyl esters without electron-donating groups. These inexpensive and convenient methods should find application in the formation of esters in complex substrates.

Friedel-Crafts Alkylation of Indoles with Trichloroacetimidates

Substituted indole scaffolds are often utilized in medicinal chemistry as they regularly possess significant pharmacological activity. Therefore the development of simple, inexpensive and efficient methods for alkylating the indole heterocycle continues to be an active research area. Reported are reactions of trichloroacetimidate electrophiles and indoles to address the challenges of accessing alkyl decorated indole structures. These alkylations perform best when either the indole or the imidate is functionalized with electron withdrawing groups to avoid polyalkylation.

Promoter free allylation of trichloroacetimidates with allyltributylstannanes under thermal conditions to access the common 1,1'-diarylbutyl pharmacophore

1,1'-Diarylbutyl groups are a common pharmacophore found in many biologically active small molecules. To access these systems under mild conditions, the reaction of diarylmethyl trichloroacetimidates with allyltributylstannanes was explored. Simply heating allyltributylstannane with the trichloroacetimidate resulted in substitution of the imidate with an allyl group. Unlike other methods used to access these systems, no strong base, transition metal catalyst, Brønsted acid or Lewis acid promoter was required to affect the transformation. Conversions are best with electron rich benzylic trichloroacetimidate systems, where excellent yields are achieved just by refluxing the reactants together in nitromethane.

Synthesis of 1,1'-Diarylethanes and Related Systems by Displacement of Trichloroacetimidates with Trimethylaluminum

Benzylic trichloroacetimidates are readily displaced by trimethylaluminum under Lewis acid promoted conditions to provide the corresponding methyl substitution product. This method is a convenient way to access 1,1'-diarylethanes and related systems, which play a significant role in medicinal chemistry, with a number of systems owing their biological activity to this functionality. Most benzylic substrates undergo ready displacement, with electron deficient systems being the exception. The use of an enantiopure imidate showed significant racemization, implicating the formation of a cationic intermediate.

Rearrangement of Benzylic Trichloroacetimidates to Benzylic Trichloroacetamides

The rearrangement of allylic trichloroacetimidates is a well-known transformation, but the corresponding rearrangement of benzylic trichloroacetimidates has not been explored as a method for the synthesis of benzylic amines. Conditions that provide the trichloroacetamide product from a benzylic trichloroacetimidate in high yield have been developed. Methods were also investigated to transform the trichloroacetamide product directly into the corresponding amine, carbamate, and urea. A cationic mechanism for the rearrangement is implicated by the available data.

Alkylation of Sulfonamides with Trichloroacetimidates under Thermal Conditions

An intermolecular alkylation of sulfonamides with trichloroacetimidates is reported. This transformation does not require an exogenous acid, base, or transition metal catalyst; instead the addition occurs in refluxing toluene without additives. The sulfonamide alkylation partner appears to be only limited by sterics, with unsubstituted sulfonamides providing better yields than more encumbered N-alkyl sulfonamides. The trichloroacetimidate alkylating agent must be a stable cation precursor for the substitution reaction to proceed under these conditions.

Lewis Acid Catalyzed Displacement of Trichloroacetimidates in the Synthesis of Functionalized Pyrroloindolines

The pyrroloindoline core is found in many natural products. These structures often differ at the C3a position, which may be substituted with an oxygen, nitrogen, or sp(3)- or sp(2)-hybridized carbon. Utilizing a trichloroacetimidate leaving group, a diversity-oriented approach to these structures has been developed. The trichloroacetimidate intermediate allows for the rapid incorporation of anilines, alcohols, thiols, and carbon nucleophiles. This method was applied in the synthesis of arundinine and a formal synthesis of psychotriasine.

Formation of DPM ethers using O-diphenylmethyl trichloroacetimidate under thermal conditions

Alcohols are effectively converted to their corresponding diphenylmethyl (DPM) ethers by reaction with O-diphenylmethyl trichloroacetimidate in refluxing toluene without the requirement of a catalyst or other additives. A number of acid and base sensitive substrates were protected in excellent yield using this new method without disturbing the pre-existing functionality present in these molecules. This reaction is the first example of the formation of an ether from stoichiometric amounts of a trichloroacetimidate and an alcohol without the addition of a Brønsted or Lewis acid catalyst.