PIFA-Mediated Oxidative Cyclization of 1-Carbamoyl-1-oximylcycloalkanes: Synthesis of Spiro-Fused Pyrazolin-5-one N-Oxides

convenient and efficient synthesis of spiro-fused pyrazolin-5-one N-oxides starting from readily available 1-carbamoyl-1-oximylcycloalkanes is developed. This general protocol features a novel and facile way for access to the five-membered azaheterocycles by formation of a new N-N single bond. The key cyclization step utilizes the formation of an N-oxonitrenium intermediate, mediated by the hypervalent iodine reagent PIFA, and its subsequent intramolecular trapping by the amide moiety under rather mild experimental conditions.

Efficient One-Pot Synthesis of Highly Substituted Thiophene Library from 1,3-Dicarbonyl Compounds

A faccile and efficient one-pot synthesis of highly substituted thiophenes has been developed and employed for the preparation of a small focused library. Treatment of 1,3-dicarbonyl compounds 1 with CS2 in the presence of K2CO3 in DMF at room temperature, followed by stepwise addition of alkyl bromides 2 and methylene active bromides 3, provided via intramolecular cyclization 2,3,4,5-tetrasubstituted thiophenes 4 in yields of 77-94%. This protocol, combining construction and modification of the thiophene ring, increases the structural diversity of final products from readily available materials. A mechanism for the one-pot synthesis of thiophenes of type 4 has been proposed. A small focused library of thiophenes is prepared using the sequential addition of reagents to achieve unique substitution in the 2 and 5 position of the thiophene ring

A Facile and Efficient One-Pot Synthesis of Substituted Quinolines from alpha-Arylamino Ketones Under Vilsmeier Conditions

An efficient one-pot synthesis of substituted quinolines from alpha-arylamino ketones in the presence of PBr3 in DMF has been developed. This general protocol provides a novel and facile access to substituted quinolines by sequential Vilsmeier-Haack reaction, intramolecular cyclization and aromatization reactions of alpha-arylamino ketones. PBr3 plays a dual role in the quinoline synthesis: as a key component of the Vilsmeier reagent (PBr3/DMF) and as a reducing reagent.

Efficient synthesis of highly substituted pyrrolin-4-ones via PIFA-mediated cyclization reactions of enaminones

A convenient and efficient synthesis of highly substituted pyrrolin-4-ones is developed via the PIFA-mediated cyclization reactions of readily available enaminones, and a mechanism involving sequential cleavage of N-C bond, formation of new N-C bond, intramolecular addition reaction, and benzilic acid type rearrangement is proposed.

One-pot synthesis of substituted isothiazol-3(2H)-ones: Intramolecular annulation of alpha-carbamoyl ketene-S,S-acetals via PIFA-Mediated N-S bond formation

A facile and efficient synthetic route towards; highly substituted isothiazol-3(2H)-ones 2 from readily available U.-carbamoyl ketene-S,S-acetals 1 is presented. The key step features the formation of an N-acylnitrenium ion, generated from the oxidization of substituted amides with the hypervalent iodine reagent phenyliodine(III) bis(trifluoroacetate) (PIFA), and its succeeding intramolecular amidation to form a new N-S bond affording the title compounds.

Large three-photon absorption and intramolecular charge transfer of the bis-donor fluorene-based molecules

Three-photon absorption (3PA) of two fluorene-based molecules with D-pi-D structural motifs (abbreviated as BPAF and BCZF) has been determined by using a Q-switched Nd: YAG laser pumped with 38 ps pulses at 1064 nm in DMF. The measured 3PA cross-sections are 222 and 140 x 10(-78) cm(6) s(2) for BPAF and BCZF, respectively. AM1 calculations show that attaching different donors changes the charge density distribution of the fluorene skeleton, and it is observed that the 3PA cross-section can be enhanced with increasing intramolecular charge transfer character, measured by the parameter Delta p(1)/Delta p(2)/Delta p(1)'. (c) 2005 Elsevier B.V. All fights reserved.

A Facile and Efficient Synthesis of Polyfunctionalized Pyridin-2(1H)-ones from β-Oxo Amides under Vilsmeier Conditions

A facile and efficient one-pot synthesis of polysubstituted pyridin-2(1H)-ones from a variety of beta-oxo amides under Vilsmeier conditions is described, and a mechanism involving sequential halogenation, formylation and intramolecular nucleophilic cyclization is proposed

Efficient and Divergent Synthesis of Fully Substituted 1H-Pyrazoles and

Efficient and divergent one-pot synthesis of fully substituted 1H-pyrazoles and isoxazoles from cyclopropyl oximes based on reaction conditions selection is reported. Under Vilsmeier conditions (POCl3/DMF), substituted 1H-pyrazoles were synthesized from 1-carbamoyl, 1-oximyl cyclopropanes via sequential ring-opening, chlorovinylation, and intramolecular aza-cyclization. In the presence of POCl3/CH2Cl2, substituted isoxazoles were obtained from the cyclopropyl oximes via ring-opening and intramolecular nucleophilic vinylic substitution (SNV) reactions

Efficient synthesis of α-alkylidene-β-lactams via NaOH-promoted intramolecular aza-Michael addition of α-carbamoyl ketene-S,S-acetals in aqueous media

A facile and efficient synthesis of substituted alpha-alkylidene-beta-lactams have been developed via a NaOH-promoted intramolecular aza-Michael addition of alpha-carbamoyl, alpha-(1-chlorovinyl) ketene-S,S-acetals and subsequent nucleophilic vinylic substitution (SNV) reaction in alcoholic aqueous media. (C) 2008 Elsevier Ltd. All rights reserved.

Vilsmeier Reaction of Enaminones: Efficient Synthesis of Halogenated Pyridin-2(1H)-ones

A facile and efficient one-pot synthesis of halogenated pyridin-2(1H)-ones from a series of readily available enaminones under Vilsmeier conditions is described, and a mechanism involving sequential halogenation, formylation, and intramolecular nucleophilic cyclization is proposed.

Copper(I)-Catalyzed Aryl Bromides To Form Intermolecular and Intramolecular Carbon-Oxygen Bonds

A highly efficient Cu-catalyzed C-O bond-forming reaction of alcohol and aryl bromides has been developed. This transformation was realized through the use of copper(I) iodide as a catalyst, 8-hydroxyquinoline as a ligand, and K3PO4 as a base. A variety of functionalized substrates were found to react under these reaction conditions to provide products in good to excellent yields.

Cyclization of citronellal to p-menthane-3,8-diols in water and carbon dioxide

A clean process has been developed for the synthesis of p-menthane-3,8-diols from cyclization of citronellal in CO2-H2O medium without any additives. With the addition of CO2, the reaction rate could be enhanced about 6 times for the cyclization of citronellal in H2O, because CO2 dissolved into water and formed carbonic acid inducing an increase of the acidity. Although, the reaction conversion in CO2-H2O is slightly lower compared to that obtained with sulfuric acid as catalyst, CO2-H2O could replace the sulfuric acid at a relative higher reaction temperature. The reaction kinetics studies showed that the hydration of isopulegols to p-menthane-3,8-diols is a reversible reaction. The equilibrium constant and the maximum equilibrium yield obtained in CO2-H2O at a range of CO2 pressures are similar to that with sulfuric acid catalyst.

Rare-earth metal complexes stabilized by amino-phosphine ligand. Reaction with mesityl azide and catalysis of the cycloaddition of organic azides and aromatic alkynes

Stoichiometric reactions between mesityl azide (MesN(3), Mes = 2,4,6-C6H2Me3) and amino-phosphine ligated rare-earth metal alkyl, LLn(CH2SiMe3) (2)(THF) (L = (2,6-C6H3Me2)NCH2C6H4P(C6H5)(2); Ln = Lu (1a), Sc (1b)), amide, LLu(NH(2,6-(C6H3Pr2)-Pr-i))(2)(THF) (2) and acetylide at room temperature gave the amino-phosphazide ligated rare-earth metal bis(triazenyl) complexes, [L(MesN(3))]Ln[(MesN(3))-(CH2SiMe3)](2) (Ln = Lu (3a); Sc (3b)), bis(amido) complex [L(MesN3)] Lu[NH(2,6-C6H3 Pr-i(2))](2) (4), and bis(alkynyl) complex (5) (L(MesN(3))Lu (C CPh)(2))(2), respectively. The triazenyl group in 3 coordinates to the metal ion in a rare eta(2)-mode via N-beta and N-gamma atoms, generating a triangular metallocycle. The amino-phosphazide ligand, L(MesN(3)), in 3, 4 and 5 chelates to the metal ion in a eta(3)-mode via N-alpha and N-gamma atoms. In the presence of excess phenylacetylene, complex 3a isomerized to 3', where the triazenyl group coordinates to the metal ion in a eta(3) mode via Na and Ng atoms.

Why [6,6]- and 1,2-Benzal-3-N-4-O-Cyclic Phenylimidate C-60 Undergo Electrochemically Induced Retro-Addition Reactions while 1,4-Dibenzyl-2,3-Cyclic Phenylimidate C-60 Does Not? C-H center dot center dot center dot X (X = N, O) Intramolecular Interactions in Organofullerenes

The electrochemical properties of a series of structurally related fullerooxazoles, [6,6] cyclic phenylimidate C-60 (1), 1,2-benzal-3-N-4-O-cyclic phenylimidate C-60 (2), and 1,4-dibenzyl-2,3-cyclic phenylimidate C-60 (3), are described, and the spectroscopic characterizations of their anionic species are reported. The results show that compounds I and 2 undergo retro-cycloaddition reactions that lead to the formation of C-60 and C61HPh, respectively, upon two-electron-transfer reduction. However, compound 3 demonstrates much more electrochemical stability as no retro-cycloaddition reaction occurs under similar conditions. Natural bond orbital (NBO) calculations on charge distribution show there is no significant difference among the dianions of 1, 2, and 3, indicating that the electrochemical stability of 3 is unlikely to be caused by the charge distribution difference of the dianions of three compounds. Examination on the crystal structure of compound 3 reveals close contacts of the C-H group with the heteroatoms (N and O) of cyclic phenylimidate, suggesting the existence of C-H center dot center dot center dot X (X = N, O) intramolecular hydrogen bonding among the addends, which is further confirmed by NBO analysis.

SOLVENT AND SUBSTITUENT EFFECTS ON THE INTRAMOLECULAR AMIDE HYDROLYSIS OF N-METHYLMALEAMIC ACID

Intramolecular amide hydrolysis of N-methylmaleamic acid is revisited at the B3LYP/6-311G(2df,p)//B3LYP/6-31G(d,p)+ZVPE level, including solvent effects at the CPCM-B3LYP/6-311G(2df,p)//Onsager-B3LYP/6-31G(d,p)+ZPVE level. The concerted reaction mechanism is energetically favorable over stepwise reaction mechanisms in both the gas phase and solution. The calculated reaction barriers are significantly lower in solution than in the gas phase. In addition, it is concluded that the substituents of the four N-methylmaleamic acid derivatives considered herein have a significant effect on the gas-phase reaction barriers but a smaller, or little, effect on the barriers in solution.