A new synthesis, including asymmetric synthesis, of alkylidenecyclopropanes by 1,2-CC insertion of cyclobutylmagnesium carbenoides as the key reaction

Treatment of 1-chlorovinyl p-tolyl sulfoxides, derived from ketones and chloromethyl p-tolyl sulfoxide, with lithium enolate of carboxylic acid tert-butyl esters gave adducts in high yields. The adducts were converted to 1-chlorocyclobutyl p-tolyl sulfoxides in four steps in high overall yields. Treatment of the 1-chlorocyclobutyl p-tolyl sulfoxides with cyclopentylmagnesium chloride in THF at −40 °C resulted in the formation of cyclobutylmagnesium carbenoids. The magnesium carbenoid 1,2-CC insertion reaction took place smoothly from the cyclobutylmagnesium carbenoids to afford alkylidenecyclopropanes in good to high yields. An asymmetric synthesis of optically active alkylidenecyclopropane was successfully achieved starting from optically active 1-chlorovinyl p-tolyl sulfoxide.     

Synthesis of new fluorescent 2-(2′,2″-bithienyl)-1,3-benzothiazoles

Bithienyl-1,3-benzothiazole derivatives were synthesised by reacting various 5-formyl-5′-alkoxy- or 5-formyl-5′-N,N-dialkylamino-2,2′-bithiophenes with ortho-aminobenzenethiol in good to excellent yields. Evaluation of the fluorescence properties of these compounds was carried out. They show strong fluorescence in the 450-600 nm region, as well as high quantum yields and large Stokes’ shifts.     

A new synthesis, including asymmetric synthesis, of spiro[4.n]alkenones from three components: cyclic ketones, chloromethyl p-tolyl sulfoxide, and acetonitrile; and a formal total synthesis of racemic acorone

1-Chlorovinyl p-tolyl sulfoxides were synthesized from several kinds of cyclic ketones and chloromethyl p-tolyl sulfoxide in good yields. Treatment of the 1-chlorovinyl p-tolyl sulfoxides with cyanomethyllithium at −78°C to room temperature gave spirocyclic enaminonitriles in high yields. Acidic treatment of the enaminonitriles afforded spiro[4.n]alkenones in good yields. By using an unsymmetrical cyclic ketone, α-tetralone, and optically active chloromethyl p-tolyl sulfoxide, this procedure afforded enantiomerically pure spiro[4.5]decenone in good yield with excellent asymmetric induction from the sulfoxide chiral center. By using this method a formal total synthesis of a racemic spirocyclic sesquiterpene, acorone, was realized.     

Copper catalyzed Gomberg-Buchmann-Hey reaction using aryldiazonium tosylate

Copper catalyzed modification of Gomberg-Bachmann-Hey reaction to synthesize symmetrical/unsymmetrical biaryls via diazotization of anilines with p-TSA and NaNO₂ system at 50 °C, in aromatic liquids as solvents and second partners was successfully developed. Aniline and 3-nitronaniline gave biphenyl and 3-nitrobiphenyl, respectively, with moderate yields. All para-substituted anilines gave comparatively higher yields while in the other cases including ortho-substituted anilines yields were lower. Except anilines with o-NHCOCH₃ and o-CONH₂ which gave symmetrical biaryls, all others gave selectively unsymmetrical biaryls.     

Coupling and cycloaddition of ynamides: homo- and Negishi coupling of tosylynamides and intramolecular [4+2] cycloaddition of N-(o-ethynyl)phenyl ynamides and arylynamides

N,N′-aryl- and N,N′-alkyl-buta-1,3-diyne-1,4-ditosylamides have been synthesized for the first time, in good to excellent yields, by copper-catalyzed dimerization of the corresponding N-aryl or N-alkyl tosylynamides. Negishi coupling of N-ethynylzinc tosylamides derivatives with (hetero)aryl iodides in the presence of Pd₂dba₃ and triphenylphosphine affords N-aryl and N-alkyl arylynamides in yields of up to 90%. Intramolecular [4+2] cycloaddition reactions of N-ethynylphenyl ynamides and arylynamides allow the synthesis of carbazoles and benzannulated and heteroannulated carbazoles in moderate-to-good yields.     

Anthracene-9-methanol—a novel fluorescent phototrigger for biomolecular caging

Photoexcitation of a solution of anthracene-9-methanol derived esters at ∼386 nm in CH₃CN/H₂O (3:2 v/v) results in fluorescence emission in the 380-480 nm range, with quantum yields of fluorescence (Φ_f) in the 0.01-0.09 range and releases of the carboxylic acids in good chemical yields (43-100%), with quantum yields of photoreaction (Φ_PR, i.e., the photodisappearance of the esters) in the 0.067-0.426 range.     

An efficient access to 3,6-disubstituted 1H-pyrazolo[3,4-b]pyridines via a one-pot double SNAr reaction and pyrazole formation

A general and efficient synthetic method for the synthesis of biologically important series of 3,6-disubstituted-1H-pyrazolo[3,4-b]pyridines was discovered. 2,6-Difluoropyridine was deprotonated using 1.1 equiv of n-BuLi in THF at <−60 °C, followed by quenching with a variety of Weinreb amides to generate 2,6-Difluoro-3-ketopyridines in high yields. A mild tandem reaction sequence of selective nucleophilic substitution of the 6-fluoride with a variety of nucleophiles, followed by hydrazine substitution of the 2-fluoride and pyrazole formation in a one-pot fashion afforded a series of 3,6-disubstituted-1H-pyrazolo[3,4-b]pyridines in moderate to good yields.     

Microwave-assisted arylation of rac-(E)-3-acetoxy-1,3-diphenylprop-1-ene with arylboronic acids

The palladium-catalyzed arylation of rac-(E)-3-acetoxy-1,3-diphenylprop-1-ene with arylboronic acids was studied under controlled microwave irradiation conditions. A variety of different catalysts, bases, and solvents were explored in order to achieve optimum yields in the shortest possible reaction times. The best isolated yields were obtained using Pd₂(dba)₃·CHCl₃/PPh₃ as the catalytic system, potassium phosphate monohydrate as the base, and toluene/H₂O as a solvent system. Microwave irradiation using 5 mol % of the palladium catalyst for 90 s (max. temp 170 °C) generally afforded the cross-coupling products in good to excellent yields.     

Silyl trifluoromethanesulfonate-activated para-methoxybenzyl methyl ether as an alkylating agent for thiols and aryl ketones

para-Methoxybenzyl methyl ether acts as an alkylating agent for thiols in the presence of trimethylsilyl trifluoromethanesulfonate and trialkylamine base in good yields (58–96%). Aryl ketones are alkylated under similar conditions, probably through an enol silane intermediate, also in high yields (67–95%). The active alkylating species is likely a p-methoxybenzyl cation.     

Microwave assisted synthesis of novel annealed porphyrins

New pyrrole derivatives (isoindoles) have been readily prepared by the reaction of an α,β-unsaturated sulfone with ethyl isocyanoacetate in the presence of tert-BuOK in good yields. The isoindoles are converted into new porphyrins which undergo retro Diels-Alder reactions under microwave irradiation at 250 °C for 4 min to give novel annealed porphyrins in quantitative yields.     

Sulfoxide-controlled SN2′ displacements between cuprates and vinyl and alkynyl epoxy sulfoxides

The S_N2′ displacement of readily available vinyl epoxy sulfoxides with organocopper reagents takes place in good yields with high anti selectivity and a good degree of E/Z stereocontrol to produce enantiopure α-hydroxy vinyl sulfoxides. A second allylic displacement on the related mesyloxy vinyl sulfoxides allows for the asymmetric construction of two adjacent chiral centers. In addition, cuprate mediated S_N2′ addition to alkynyl epoxy sulfoxides affords α-hydroxy allenyl sulfoxides in good yields.     

An amide orthoesterification route to N-(1′-alkylthioglucopyranosyl)indoles

The addition of 3-methylindolylmagnesium bromide to tetra-O-benzyl-α-d-gluconothionolactone yields the expected indole N-gluconothioamide as its hemiorthothioamide tautomer. The thiol function is alkylated to yield the corresponding orthothioamide, a 1′-alkylthio-substituted N-glycoside. Alternatively, the 1′-alkylthio-N-glycoside can be accessed from the corresponding indole N-gluconamide via a boron trifluoride-etherate mediated orthoesterification with ethanethiol. Radical reduction of the orthothioamide yields the N-glycosides in 2:1 stereoselectivity in favor of the β-N-glycoside, while reduction via the oxonium ion leads to an improved 6:1 selectivity.     

BF3·OEt2-catalyzed synthesis of 1-(tetrahydropyran-3-yl)-1,3-dihydroisobenzofuran and trans-fused hexahydropyrano[3,2-c]chromene derivatives

A novel intramolecular Prins cyclization of (E)-5-(2-(hydroxymethyl)phenyl)pent-4-en-1-ol with aldehydes has been achieved using 10 mol % BF₃·Et₂O to produce 1-(tetrahydropyran-3-yl)-1,3-dihydroisobenzofuran derivatives in good to excellent yields with high selectivity. Similar type of coupling with salicylaldehydes provides the trans-fused hexahydropyrano[3,2-c]chromene derivatives in excellent yields.     

Efficient and convenient synthesis of spiroindolinone-quinazolines induced by stannous chloride

An efficient, convenient, one-pot synthesis of 1′H-spiro[indoline-3,2′-quinazoline]-2,4′(3′H)-dione derivatives was accomplished in good yields via the novel reductive cyclization of 2-nitrobenzamides and isatins mediated by SnCl₂·2H₂O system. A variety of substrates can participate in the process with good yields, making this methodology have broad applicability. The structure of compound 3c has been confirmed by X-ray diffraction analysis.     

Novel diastereoselective synthesis of (E)- and (Z)-allylsilanes via organoboranes

A simple, novel diastereoselective synthesis of both (E)- and (Z)-allylsilanes via organoboranes is developed. (E)-1-Alkenylboronate esters easily prepared from the corresponding terminal alkynes via hydroboration with dibromoborane-methyl sulfide complex followed by treatment with 1,3-propane diol readily react with trimethylsilylmethyllithium at −78 °C in methanol followed by reaction with iodine in methanol to produce the corresponding (Z)-allylsilanes in high yields (72-80%) and in high stereochemical purities (98% as evidenced by CMR spectral data). Similarly, the (Z)-1-alkenylboronate esters react with trimethylsilylmethyllithium at −78 °C in methanol followed by treatment with iodine in methanol to produce the corresponding (E)-allylsilanes in moderate yields (57-65%) in high stereochemical purities (>98% as revealed by CMR spectral data).     

An effective synthesis of N,N-dimethylamides from carboxylic acids and a new route from N,N-dimethylamides to 1,2-diaryl-1,2-diketones

Carboxylic acids were heated at 150 °C in DMF in the presence of 1.25 equiv of thionyl chloride to give corresponding N,N-dimethylamides in good yields. Tandem chlorination and amidation reactions occurred in the one-pot procedure. Dicarboxylic acids needed prolonged reaction time to produce bisamides in good yields. Some benzamides were efficiently converted into corresponding 1,2-diaryl-1,2-diketones (benzils) under acyloin condensation conditions in the presence of 4,4′-di-tert-butylbiphenyl (DBB) in THF. Ultrasonic irradiation effectively accelerates the reaction, but it is not critical. However, the presence of DBB is fatal to the reaction. Although a few synthetic methods for benzils from benzoic acids have been reported so far, this method is one of the most convenient and highly reproducible procedures.     

A new method for making acyl fluorides using BrF3

While many carboxylic acids could be converted directly to acyl fluorides by using BrF₃, the reaction with acyl chlorides was found to be of a more general nature and yields better results. Surprisingly, reacting t-butyl esters with bromine trifluoride also resulted in acyl fluorides in reasonable yields. The reactions were completed in a few seconds at 0 °C.     

The difference in reactivity of (−)-mono and dimenthyl vs. diethyl alkylphosphonates in the α-lithiation reaction: Carbanionic synthesis of unknown (−)-dimenthyl 1-iodoalkylphosphonates and their first use in the radical iodine atom transfer addition (I-ATRA) and cyclisation (I-ATRC) reactions

Unknown (−)-dimenthyl and ethyl (−)-menthyl 1-iodoethylphosphonates were synthesized via 1-lithio derivatives in 85-87% yields. Starting (−)-dimenthyl alkylphosphonates (R = Me, Et, i-Pr) were obtained in the Michaelis-Becker reaction (75-81% yields) and/or in the methylation reaction of the corresponding 1-lithio-alkylphosphonates (78-92% yields). An interesting concentration and time correlations, never observed for diethyl alkylphosphonates, were found for the metalation of bulky (−)-menthyl alkylphosphonates with n-BuLi and general reaction conditions for the carbanion generation were elaborated. The first example of the I-ATRA reaction of (−)-dimenthyl 1-iodoethylphosphonate with 1-hexene (AIBN) gave four diastereomers (1.6:1:1:0.4), separated into two pairs. The I-ATRC reaction was not effective due to a steric hindrance around the reactive center. The X-ray analysis of (−)-dimenthyl methylphosphonate confirmed a considerable steric hindrance in higher (−)-dimenthyl alkylphosphonate esters in comparison to their diethyl analogs.     

[3+2] Dipolar cycloadditions of an unstabilised azomethine ylide under continuous flow conditions

The [3+2] dipolar cycloaddition reactions of the unstabilised azomethine ylide precursor benzyl(methoxymethyl)(trimethylsilylmethyl)amine with 12 electron-deficient alkenes in the presence of catalytic trifluoroacetic acid are examined under continuous flow conditions (20-100 °C, 10-60 min residence time). The more reactive and hazardous alkenes such as ethyl acrylate, N-methylmaleimide and (E)-2-nitrostyrene afford substituted N-benzylpyrrolidine products in 77-83% yields, whereas less reactive dipolarophiles such as (E)-crotononitrile and ethyl methacrylate give lower yields (59-63%). Under optimised conditions, the reaction with ethyl acrylate is scaled up to afford ethyl N-benzylpyrrolidine-3-carboxylate (30 g, 87%) in 1 h.     

Alkenylation of thiophenes at the 2-position with magnesium alkylidene carbenoids

Treatment of magnesium alkylidene carbenoids, generated from 1-chlorovinyl p-tolyl sulfoxides with isopropylmagnesium chloride at −78 °C in toluene, with 2-lithiothiophenes gave 2-alkenylated thiophenes in good to high yields. The intermediate of this reaction was found to be an alkenylmagnesium, which could be trapped with iodoalkanes and ethyl chloroformate. This procedure offers a novel and efficient one-pot synthesis of thiophenes having a disubstituted or a trisubstituted olefin at the 2-position from thiophenes in good yields.