(Z)-2,2-Dimethyl-5-carboxymethylene-1,3-dioxolan-4-one: a new synthon for the synthesis of α,γ-diketoacid derivatives

The synthesis and reactivity of (Z)-2,2-dimethyl-5-carboxymethylene-1,3-dioxolan-4-one, a new and versatile synthon useful for the synthesis of selectively protected α,γ-diketoacid derivatives, are described. This new, protected form of hydroxyl fumaric acid along with its acid chloride was used to prepare ester, amide, and aryl derivatives. The dioxolane moiety was found to be a convenient functionality that facilitated ready unmasking by straightforward hydrolysis to reveal α,γ-diketoacid derivatives or derivatization to yield ester, amide, and 2,3-pyrrolidinedione derivatives.     

A formal method for the de-N,N-dialkylation of Sommelet–Hauser rearrangement products

Selective amine de-alkylation enables the conversion of Sommelet–Hauser rearrangement products into 2-aryl-2-bromoacetic acid derivatives. These compounds are valuable synthetic intermediates in the synthesis of α-aryl-α-amino or α-aryl-β-amino acid derivatives. The method presented herein is a formal de-N,N-dialkylation of Sommelet–Hauser rearrangement products.     

N-Hydroxymethyl derivatives of α-amino aldehydes used for the stereoselective syntheses of β-amino-α-hydroxy acids

The N-hydroxymethyl derivatives of α-amino aldehydes 1 were utilized for the effective synthesis of several β-amino-α-hydroxy acid derivatives in a one-pot process starting from the corresponding α-amino aldehydes. Properly protected methyl esters 3 were prepared in 65–79% yields from α-amino aldehyde derivatives 1 with more than 20:1 stereoselectivity. The application of suitably protected β-amino-α-hydroxy esters was shown by an efficient synthesis of the bioactive peptide, bestatin, and its more potent analogue, AHPBA-Val, in high yields from ent-3a.     

A new method for generation of non-stabilized α-amino-substituted carbanions by the reaction of magnesium carbenoids with N-lithio arylamines: their reactivity and a new synthesis of α-amino acid derivatives

Magnesium carbenoids were generated from aryl 1-chloroalkyl sulfoxides with i-PrMgCl in THF at low temperature in quantitative yields. The magnesium carbenoids were found to be reactive with N-lithio alkylamines to afford an olefin, which was derived from dimerization of the magnesium carbenoid, in moderate yield. On the other hand, reaction of the magnesium carbenoids with N-substituted N-lithio arylamines gave non-stabilized α-amino-substituted carbanions in good yields. Reactivity of the α-amino-substituted carbanions with some electrophiles was investigated and it was found that ethyl chloroformate reacted to give α-amino acid derivatives in good yields. As a whole, a new method for one-pot, three-component combined synthesis of α-amino acid derivatives from aryl 1-chloroalkyl sulfoxides was realized.     

Solid-phase synthesis of imidazo[1,2-a]pyridines and imidazo[1,2-a]pyrimidines

The synthesis of imidazo[1,2-a]pyridine and imidazo[1,2-a]pyrimidine derivatives by condensation between an α-bromoketone bound to solid support and various 2-aminopyridine or 2-aminopyrimidine derivatives was described. Either an acid labile linker or a base labile linker was used in this study.     

Synthesis of pyrrolizidine-and indolizidinedione derivatives based on N-phthalylaspartic acid

A procedure was developed for the synthesis of pyrrolizidine-and indolizidinediones derivatives from the keto-stabilized sulfonium α-and β-ylides of N-phthalylaspartic acid.     

Facile synthesis of α-hydroxy carboxylic acids from the corresponding α-amino acids

An effective and improved procedure is developed for the synthesis of α-hydroxy carboxylic acids by treatment of the corresponding protonated α-amino acid with tert-butyl nitrite in 1,4-dioxane–water. The amino moiety must be protonated and located α to a carboxylic acid function in order to undergo initial diazotization and successive hydroxylation, since neither β-amino acids nor acid derivatives such as esters and amides undergo hydroxylations. The method is successfully applied for the synthesis of 18 proteinogenic amino acids.     

An asymmetric synthesis of carboxylic acid derivatives,including lactic acid and α-amino acid derivatives,from optically active 1-chlorovinyl p-tolyl sulfoxides and ester lithium enolates with creation of chirality at the α-position

Treatment of optically active 1-chlorovinyl p-tolyl sulfoxides, which were synthesized from symmetrical ketones or methyl formate and (R)-(−)-chloromethyl p-tolyl sulfoxide in three steps, with lithium enolate of carboxylic acid tert-butyl esters gave optically active adducts having a substituent (alkyl, alkoxy, or dibenzylamino group) at the α-position with high 1,4-chiral induction from the sulfur chiral center. The adducts were converted to optically active esters, lactic acid, and α-amino acid derivatives having a chiral center at the α-position. When this addition reaction was carried out with an ester enolate generated from excess carboxylic acid tert-butyl ester with LDA in the presence of HMPA, the diastereomer of the adduct was obtained. By using the two reaction conditions for the generation of the ester enolate, a new method for asymmetric synthesis of both enantiomers of carboxylic acid derivatives having a substituent at the α-position from the one chiral source, (R)-(−)-chloromethyl p-tolyl sulfoxide, was achieved.     

Direct access to 3-substituted 1,4-oxathiepino[5,6-b]pyridine-5-one through one-pot substitution cyclization reaction of 2-mercapto-3-nicotinic acid with α-bromo ketones

A direct, one-pot synthesis route to [1,4]oxathiepino[5,6-b]pyridin-5-one derivatives was optimized by reacting different α-bromo ketones with 2-mercaptonicotinic acid. The advantages of this method include high efficiency, regioselective, and multistep conversion in a single-pot protocol. These types of pyridine annulated[1,4]oxathiepin-5-one derivatives are described here for the first time and seem to be interesting candidates for screening purpose. The presented protocol is suitable for using rare chemicals for synthesis of such derivatives.     

Highly enantioselective allylic alkylation of 5H-oxazol-4-ones with Morita-Baylis-Hillman carbonates

An organocatalytic enantioselective allylic alkylation of 5H-oxazol-4-ones with Morita-Baylis-Hillman carbonates has been developed. With 10?mol% of commercially available cinchonidine, a wide range of substituted 5H-oxazol-4-one derivatives were constructed in good-to-excellent yields with high diastereo- and enantioselectivities. The allylic alkylation adducts obtained are valuable precursors for the synthesis of chiral α-alkyl α-hydroxycarboxylic acid derivatives, which represent a series of versatile building blocks in many biologically active compounds.     

Convergent total synthesis of (−)-dactylolide

A convergent total synthesis of (?)-dactylolide is described. Constructing the 2,6-disubstituted exo-methylene THP moiety was achieved by the intramolecular allylation of α-acetoxy ether. The cyclization precursor was prepared from two segments, an alcohol and carboxylic acid derivatives, by esterification followed by reductive acetylation.     

Reaction of magnesium cyclopropylidene with N-lithio arylamines: a method for generation of α-amino-substituted cyclopropylmagnesiums and a study for their reactivity with electrophiles

Magnesium cyclopropylidene was generated from 1-chlorocyclopropyl phenyl sulfoxide with i-PrMgCl in THF at −78 °C in high yield by a sulfoxide-magnesium exchange reaction. The generated magnesium cyclopropylidene was found to be reactive with N-lithio arylamines to give α-amino-substituted cyclopropylmagnesiums. The reaction of the α-amino-substituted cyclopropylmagnesiums with several electrophiles was examined and a new method for a synthesis of cyclopropane amino acid derivatives was realized.     

Total syntheses of chaetocin and ent-chaetocin

The first total synthesis of chaetocin (1), a potent histone methyltransferase inhibitor, is described in detail. Key reactions were radical bromination for α-oxidation of the diketopiperazine ring, and reductive radical coupling for construction of the dimeric core structure. Stereoselective construction of the disulfide bridges was achieved via substitution reaction with H₂S. The total synthesis of 1 was accomplished in nine steps starting from known d-amino acid derivatives. Total synthesis of non-natural ent-chaetocin (ent-1) was also achieved via the established synthetic route, starting from l-amino acid derivatives.     

A novel synthesis of cyclic α-amino aldehydes, amino alcohols, and α-amino acid methyl esters from cyclic ketones through sulfinylaziridines

Treatment of 1-chlorovinyl p-tolyl sulfoxides, which were synthesized from cyclic ketones and chloromethyl p-tolyl sulfoxide in three steps in good yields, with N-lithio arylamines gave sulfinylaziridines in high yields. On treatment with N-lithio aniline or N-lithio p-chloroaniline, the sulfinylaziridines gave α-amino aldehydes in high yields. The α-amino aldehydes were converted to amino alcohols and α-amino acid methyl esters in moderate to good yields. This procedure offers an efficient method for synthesis of cyclic α-quaternary α-amino aldehydes, amino alcohols, and α-amino acid derivatives from cyclic ketones.     

Efficient asymmetric synthesis of α-alkylated benzylic methyl sulfonates

The first highly efficient auxiliary-controlled synthesis of various α-substituted sulfonic acid derivatives is described. Alkyl or aryl halides were reacted with lithiated benzylic sulfonic esters bearing 1,2:5,6-di-O-isopropylidene-α-d-allofuranose as a removable enantiopure alcohol auxiliary to give the alkylated products in excellent diastereomeric excesses. The racemization-free cleavage conditions provided highly enantioenriched sulfonic acid derivatives (ee≥98%).     

α-Amido sulfones from natural α-amino acids and their reaction with carbon nucleophiles

Amides obtained from N-carbamoyl α-amino acids react with aldehydes in the presence of benzenesulfinic acid to give α-amido sulfones in good yield. These derivatives act as equivalents of N-acylimines in the reaction with nucleophiles leading to the corresponding addition products. The utilization of the lithium enolate of alkyl acetates as a nucleophile allows the preparation of α,β-dipeptides, while a two-step procedure involving nitromethylation and Nef conversion leads to the synthesis of α,α-dipeptides.     

Synthesis of (E)-prop-1-ene-1,3-diyldibenzene derivatives via direct decarboxylative coupling of α,β-unsaturated carboxylic acids with benzyl boronic acid pinacol ester

The first copper-catalyzed cross-coupling reaction between benzyl boronic acid pinacol ester and α,β-unsaturated carboxylic acids was described. The ready availability of the starting materials and excellent E selectivity make this protocol a safe and operationally convenient strategy for the efficient synthesis of (E)-prop-1-ene-1,3-diyldibenzene derivatives.     

A facile synthesis of 3-aryl pyroglutamic acid. Facile synthesis of baclofen and chlorpheg

A facile synthesis of 3-aryl pyroglutamic acids via stepwise [3+2] annulation and desulfonated hydrolysis is reported. Base-induced coupling/cyclization reactions of α-sulfonylacetamide with various β-functional groups of (Z)-2-bromoacrylates yielded three contiguous chiral centers on the polysubstituted pyroglutamates system with trans-trans orientation in a one-pot synthesis. This facile strategy was used to synthesize amino acid derivatives baclofen and chlorpheg.     

Synthetic studies of decursivine derivatives: preparation of key indole alkaloids via α-hydroxyalkylation

2-Hydroxyacetyl indole modified at C-3 position was prepared with an eye to developing a total synthesis of decursivine derivatives (decursivine, serotobenine, moschaminindolol, and flavumindole). The indole was prepared through a sequence of oxalyl chloride introduction at C-3 position of indole and acid chloride reduction with tributyltin hydride. In addition, we report a novel synthesis of fully functionalized Uhle's ketone via ortho-selective α-hydroxyalkylation.     

Chameleonic reactivity of α-amino nitrile-derived ureas. Synthesis of highly functionalized imidazolidin-2-one and imidazolidine-2,4-dione derivatives

The potential of α-amino nitrile-derived ureas for the synthesis of imidazolidin-2-one derivatives has been studied in the context of a medicinal chemistry project focused on the search of antagonists of the thrombin receptor PAR1. In this study α-amino nitrile-derived ureas have shown chameleonic reactivity. Thus, under neutral, basic or mild acid media they cyclize to 4-iminoimidazolidin-2-one derivatives, which tautomerize to 4-amino-2,3-dihydro-1H-imidazol-2-ones. This tautomerism triggers epimerization at the C₅ of the imidazolidine ring, as well as its oxidation. However, they give stable highly functionalized hydantoin derivatives under strong acid media, by a no-epimerizing two-step hydrolysis.