High yielding selective access to spirocyclopropanated 5-oxopiperazine-2-carboxylates and 1,4-diazepane-2,5-diones from methyl 2-chloro-2-cyclopropylideneacetate

The 2-spirocyclopropanated methyl 5-oxopiperazine-2-carboxylate and the 3-spirocyclopropanated 6-chloro-1,4-diazepane-2,5-dione could both be prepared at choice in 93 and 88% yield, respectively, from methyl 2-chloro-2-cyclopropylideneacetate () in a sequence of Michael addition of 3-benzyloxypropylamine, peptide coupling with N-Boc-glycine, Boc-group removal and cyclization. Transformation of the benzyloxypropyl side chain, peptide coupling with N-Boc-(S)-asparagine, deprotection and repeated cyclization led to the octahydro[2H]pyrazino[1,2-a]pyrazinetrione scaffold containing a rigidified mimic of a tripeptide with a DGR motif. The overall yield of after deprotection of (a total of 13 steps in 8 distinct operations) was 30%.     

An efficient method to access 2-fluoroalkylbenzimidazoles by PIDA oxidation of amidines

A mild and practical strategy for the synthesis of 2-bromodifluoromethyl (or trifluoromethyl)-1H-benzimidazoles via PIDA-mediated oxidative intramolecular cyclization of the fluorinated amidines is described. The approach has the advantages of superior yields, excellent functional groups tolerance and mild reaction conditions.     

Synthesis of methyl 2-aryl-5-chlorosulfonyl-1,3-oxazole-4-carboxylates and their reactions with amines and amidines

Previously unknown methyl 2-aryl-5-chlorosulfonyl-1,3-oxazole-4-carboxylates have been synthesized. Their reactions with amines and amidines have yielded the corresponding sulfonamides and 6H,7H-[1,3]oxazolo-[5,4-d]pyrimidin-7-ones.     

SrCl2 as an efficient cocatalyst for acidic hydrolysis of methyl glycosides

SrCl2 was found to be the most efficient cocatalyst for the acidic hydrolysis of methyl glycosides after 26 kinds of most representative metal salts were screened. The SrCl2-cocatalyzed acidic hydrolysis of methyl glycosides is highlighted by short reaction times, less byproducts and high yields. A possible mechanism for the SrCl2-cocatalyzed hydrolysis is also proposed.     

Regioselectivity in reactions of alkynylmetal complexes with pyrimidinones

Regioselectivity is observed in $\text{1}\text{1}$-adduct formation between phenylethynyltriisopropoxytitanium and 2(1/H)-pyrimidinones; the new carbon-carbon bond is formed at C(4). In contrast the 3,4- and 3,6-dihydro products are formed together from the corresponding magnesium and lithium reagents, but from the magnesium compound the major product is the 3,6-dihydro isomer. Ethynylmagnesium bromide gives equimolar amounts of the 3,4- and 3,6-dihydro isomers. Dehydrogenation of the products gives the alkynylated aromatic heterocycles.     

Modified Shapiro reactions with bismesitylmagnesium as an efficient base reagent

Bismesitylmagnesium has been shown to successfully mediate the Shapiro reaction. A range of tosylhydrazones has been subjected to the developed system, which furnishes exceptionally high incorporation of the introduced electrophiles and good yields of the functionalized styrenes. At conveniently accessible temperatures and with a comparably small excess of base reagent, this protocol offers an efficient alternative to the lithium-mediated process. Importantly, 1.05 equiv of Weinreb amides are sufficient to obtain aryl enones in good yields.     

Domino reactions of 2-methyl chromones containing an electron withdrawing group with chromone-fused dienes

Domino reactions of 2-methyl substituted chromones containing an electron withdrawing group at the 3-position with chromone-fused dienes synthesized a diverse range of benzo[a]xanthones and complicated chromone derivatives. These multiple-step reactions result in either two or three new C-C bonds without a transition metal catalyst or an inert atmosphere.     

Pd(OAc)(2)-catalyzed Domino reactions of 1-chloro-2-haloarenes and 2-haloaryl tosylates with hindered Grignard reagents via palladium-associated arynes

The palladium-associated aryne generation strategy and Pd(OAc)(2)-catalyzed annulative Domino reactions of 1-chloro-2-halobenzenes and 2-haloaryl tosylates with hindered Grignard reagents via palladium-associated arynes are described. The palladium-associated aryne generation strategy described here not only allows the high yield, one-step access to potentially useful substituted fluorenes from readily available 1-chloro-2-halobenzenes and 2-haloaryl tosylates, but may also lead to the development of other tandem reactions based on these readily available ortho leaving group bearing haloarenes. [reaction: see text]     

Domino Michael-Aldol reactions on 1,4-diarylbut-2-ene-1,4-diones with methyl acetoacetate furnish methyl 2-aroyl-4- hydroxy-6-oxo-4-arylcyclohexane-1-carboxylate derivatives

Domino Michael-Aldol reactions on 1,4-diaryl-2-butene-1,4-diones with methyl acetoacetate in the presence of activated Ba(OH)(2) furnished methyl (1R*,2S*,4S*)-2-aroyl-4-hydroxy-6-oxo-4-arylcyclohexane-1-carboxylate derivatives in a stereo- and regiospecific manner. While treatment of these cyclohexanecarboxylate products with TsOH resulted in the dehydrated and decarbomethoxylated cyclohexenone derivatives, the reaction with NaOMe furnished 3,5-disubstituted phenols via dehydration, decarbomethoxylation, and dehydrogenation. NaCl/DMSO under microwave irradiation transformed the cyclohexanecarboxylate products to the 7-hydroxyisobenzofuranone derivatives.     

Reaction of methyl 3-phenyl-3-chloro-2-oxopropionate with thiosemicarbazones

The reaction of methyl 3-phenyl-3-chloro-2-oxopropionate with thiosemicarbazones proceeds via the intermediate formation of methyl [S-(1-alkylideneisothiosemicarbazidyl)]-3-phenyl-2-oxopropionate hydrochlorides, which then cyclize to novel 4-methoxycarbonyl-5-phenyl-2-substituted thiazoles. Hydrolysis of the intermediate products and the thiazoles obtained therefrom with simultaneous distillation of the carbonyl compound affords 2-hydrazino-4-methoxy-carbonyl-5-phenylthiazole.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1422–1426, June, 1991.     

An efficient method for the synthesis of 2-thiazoleacetic acid N-sulfonyl amidines

Chemistry of Heterocyclic Compounds - A three-step method was designed and developed on the basis of retrosynthetic analysis for the synthesis of hybrid molecules containing a thiazole ring and an...     

Domino reactions starting from alkynyl esters tethered to 2-methyl-1,3-cycloalkanediones. Efficient access to polyfunctionalized diquinanes, allenoates, and oxetanes

The reactivity of alkynyl esters tethered to 2-methyl-1,3-cycloalkanediones toward TBAF and TBAF in the presence of 4 Å molecular sieves is reported. Polyfunctionalized diquinanes, allenaotes or oxetanes resulting from anionic domino reactions can be readily available with high to complete diastereoselectivities.     

Domino reactions that combine an azido-Schmidt ring expansion with the Diels-Alder reaction

[reaction: see text] The combination of the intramolecular Schmidt reaction with the Diels-Alder reaction provides expedient access to a variety of heterocycles. Two different modes of reaction planning are presented. In one, the azide and ketone moieties necessary for the intramolecular Schmidt reaction originate on different molecules that are reacted and subsequently undergo a ring-adjustment step. Alternatively, an azido ketone can be used provided the ketone is deactivated by its presence in an enone.     

Facile and efficient access to 2,6,9-tri-substituted purines through sequential N9, N2 Mitsunobu reactions

A facile, efficient and mild synthesis of 2,6,9-tri-substituted purines is presented, starting from commercially available 2-amino-6-chloropurine, which employs sequential N9 then N2 Mitsunobu reactions as key steps. Importantly, our synthetic approach to N2-functionalization of the purine nucleus obviates the harsh conditions required by the traditional nucleophilic aromatic substitution of a 2-halo group with primary amines. Benzylic, allylic, propargylic and aliphatic alcohols all coupled in very good to excellent yields in both Mitsunobu reactions. Significantly, excellent chemoselectivity and N9-regioselectivity were observed for the first coupling, and reactions were complete within 15 min at room temperature. Our novel methodology may be readily adapted to furnish N⁹-mono- or N²,N⁹-di-functionalized guanine analogues, and the utility of our protocol is further demonstrated by the efficient synthesis of the CDK inhibitor bohemine.     

Dihydrofuropyridines in reactions of pyridoxal imine with 2-chloro-1,3,2-dioxaphosphorinanes

Russian Journal of General Chemistry -     

Domino process optimized via ab initio study for an alternative access to bicyclic lactams

A totally new acid-free domino process to access highly functionalized bicyclic γ- and δ-lactams starting from commercially available and inexpensive ethoxymethylene derivatives is reported. Mechanisms elucidated by computational calculations led to new reaction conditions that boosted the yields up to 3.5 times higher.     

Pd-EDTA as an efficient catalyst for Suzuki-Miyaura reactions in water

PdCl₂-EDTA complex 1 is an efficient catalyst for the Suzuki-Miyaura reactions of aryl and heteroaryl halides with aryl(heteroaryl)boronic acids in water at 20-100 °C. Aryl iodides and bromides undergo the cross-coupling with turnover numbers (TON) up to 97,000 and turnover frequencies (TOF) up to 582,000 h⁻¹.     

Nafion as an efficient reaction medium for diastereoselective photochemical reactions

The ability of alkali ion exchanged Nafion interior to enhance the influence of chiral auxiliaries in photochemical reactions was examined with three independent asymmetric photoreactions, namely, photoisomerization of trans,trans-2,3-diphenylcyclopropane-1-carboxylic acid derivatives, electro-cyclization of 2-oxo-1,2-dihydropyridine-1-acetic acid derivatives and oxa di-π methane rearrangement of 1,2-dihydro-2,2′-dimethylnapthalenone derivatives. Chiral auxiliaries that lead to 1:1 mixture of diastereomers in organic solvents yielded products in 5-21% diastereomeric excess when the photoreactions were carried out within the nanoclusters of alkali ion exchanged Nafion. The investigated systems also serve as probes to understand the mode of distribution of guest molecules within Nafion framework upon inclusion.     

2-aryl-N-tosylazetidines as formal 1,4-dipoles for [4 + 2] cycloaddition reactions with nitriles: an easy access to the tetrahydropyrimidine derivatives

[reaction: see text] A new synthetic route to 2-aryl-N-tosyl azetidines has been developed starting from N-tosylarylaldimines in two steps in an overall yield of 63-70%. A formal [4 + 2] cycloaddition of these 2-aryl-N-tosylazetidines with nitriles in the presence of BF3.OEt2 has been described for the synthesis of substituted tetrahydropyrimidines. It is proposed that the reaction proceeds in Ritter fashion.     

Synthesis of (R)-dihydropyridones as key intermediates for an efficient access to piperidine alkaloids

The efficient transformation of D-glucal to (2R)-hydroxymethyldihydropyridinone 5 in seven steps and 35 % overall yield is reported. Dihydropyridone 5 constitutes a versatile chiral building block for the synthesis of various piperidine alkaloids. In this regard, 5 was converted to piperidinol 13 and piperidinone 15, that may be further elaborated for the syntheses of (+)-desoxoprosophylline (1) and deoxymannojirimycin (3) or D-mannolactam (4), respectively.