Retrievable magnetic copper ferrite nanoparticles: an efficient catalyst for air oxidative cyclization of bisnaphthols

Herein, a green and efficient heterogeneous and photocatalytic system for the oxidation of bisnaphthols in acetonitrile under light-emitting diode will be presented. In this reaction, aerial oxygen and H₂O₂ have been used as oxidant in the presence of copper ferrite nanoparticles and N-hydroxyphthalimide as an organic co-catalyst. Copper ferrite nanoparticles were magnetically separated, the efficiency of which remained nearly unchanged up to five cycles. Magnetic copper ferrite nanoparticles were synthesized by sol–gel method and characterized by XRD, FT-IR, SEM, TEM, VSM and DRS analysis. In this project, both sets of diastereomers were formed.

Graphical abstract

Catalytic system for the oxidation of bisnaphthols.

     

Ruthenium-catalyzed oxidative cyclization of 1,7-dienes. A novel diasteroselective synthesis of 2,7-disubstituted trans-oxepane diols

The ruthenium-catalyzed oxidation of some representative 1,7-dienes has been investigated. Tetrasubstituted 1,7-dienes are transformed into the corresponding trans-2,7-bis-hydroxyalkyl-oxepanes through an oxidative cyclization process. The process proceeds with an excellent stereoselectivity level.     

Photo- and thermochromic spirans

The mechanisms of the valence isomerization of 2H-pyrans and chromene were calculated by means of the MINDO/3 method. A correlation between the magnitude of the barrier of activation of the electrocyclic reaction and the differences in the energies of the bonds of the tautomeric forms was noted. A simple scheme that makes it possible to estimate the magnitude of the activation barrier of the thermochromic transformations of spiropyrans on the basis of quantum-chemical calculations by the Pariser-Parr-Pople (PPP) method is proposed.See [1] for Communication 16.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 172–177, February, 1988.The authors thank V. A. Lokshin and N. A. Voloshin for providing us with data on the barriers of thermochromic transformations of spiropyrans.     

Oxidation of bisnaphthols to spironaphthalenones,revisited

Bis(2‐hydroxy‐1‐naphthyl)methane derivatives have been efficiently converted to their corresponding spirans through three methods, i.e. oxidation by TCCA under mild reaction conditions, Ph₃Bi catalyzed air oxidation, and by electrochemical reaction. The first two methods are diastereoselective and give either of the two possible diastereomers, while the electrochemical method produces equal amounts of these diastereomers.     

Facile oxidative cyclization and carbonylation of allylicalcohols

Palladium chloride catalyzed reaction [room temperature, one atmosphere] of primary, secondary, and tertiary allylic alcohols with carbon monoxide and oxygen, hydrochloric acid, and cupric chloride in tetrahydrofuran affords five-membered ring lactones.     

Photochromic and thermochromic spirans

New spiropyrans of the 4-oxo-3,4-dihydro-2H-1,3-benzoxazine series, individual representatives of which have photochromic properties, were obtained by condensation of 2-alkyl-4-oxo-1,3-benzoxazinium perchlorates with aromatic o-hydroxy aldehydes in acetic acid and subsequent treatment of the 2-(o-hydroxystyryl) derivatives with pyridine or triethylamine. The structures of the synthesized compounds were confirmed by the PMR, IR, and UV spectroscopic data.See [1] for communication VI.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 161–166, February, 1978.     

Photochromic and thermochromic spirans

By means of the SCF MO LCAO method in the π-electronic (PPP) and all-valence (CNDO) approximations the electronic structures and spectral characteristics of the valence isomers of 2H-chromenes, thiochromenes, and 1,2-dihydroquinolines have been calculated. On the basis of a consideration of the electronic configuration of various excited states, an explanation has been given of the mechanism of the photochromism of the chromenes and their analogs. A hypothesis has been put forward concerning the possibility of thermochromism in 1,2-dihydronaphthalene. It has been shown that the diffuseness of the long-wave absorption band of the open forms of the compounds investigated is not connected with the existence of several stereoisomers. The influence of the heteroatom and of benzo-fusion on the long-wave absorption has been analyzed. The nature of the electronic transition responsible for the long-wave absorption of the photo-colored forms has been explained.     

Radical oxidative cyclization of spiroacetals to bis-spiroacetals: an overview

The use of iodobenzene diacetate and iodine under photolytic conditions provides and efficient method for the oxidative cyclization of spiroacetals bearing an hydroxyalkyl side chain to bis-spiroacetals. An overview is provided of the use of this reaction for the synthesis of several bis-spiroacetal containing natural products such as the polyether antibiotics salinomycin and CP44,161 and the shellfish toxins, the spirolides.     

Photo- and thermochromic spirans

New spiropyrans with -acceptor azomethine and ketovinyl substituents in the 8 position were synthesized using the functional possibilities of the carbonyl group. The structures of the compounds obtained and their photochromic properties in 2-propanol at –70°C were studied.For Communication 17 see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 176–179, February, 1993.     

Regiospecific oxidative cyclization of n-methylsulfonylamines into pyrrolidines

In the framework of the approach to remote oxidative functionalization of organic compounds of various classes, which is currently under exploration by us and which is based on reactions of element-centred free radicals, the regiospecific oxidative cyclization of N-methylsulfonylalkylamines $\text{3}$ into N-methylsulfonylpyrrolidines $\text{4}$ has been accomplished. The more facile isomerisation of intermediate sulfonamidyl radicals $\text{8}$ with 1,5-H shift in comparison with their carboxamidyl analogues $\text{16}$ is, in our opinion, the chemical proof of different electronic configurations of radicals $\text{8}$ (σ structure) and $\text{16}$ (predominantly π structure) generated under identical conditions using Na ₂S₂O₈CuCl₂ system.     

Copper(II)-mediated oxidative cyclization of enamides to oxazoles

The copper(II)-mediated oxidative cyclization of enamides to oxazoles is reported. A range of 2,5-disubstituted oxazoles were prepared in moderate to good yields in two steps from simple amide and alkyne precursors.     

The oxidative cyclization of n-phenyl-3-methylthiopropylamines to form N-phenyl-s-methylisothiazolidinium salts

A series of N-phenyl-3-methylthiopropylamine hydrochlorides were prepared by reacting a series of anilines with methional and sodium cyanoborohydride. These were cyclized upon oxidation by N-chloro-succinimide to the corresponding N-phenyl-S-methylisothiazolidinium derivatives which were isolated as the tetraphenylborate salts. Compounds successfully prepared included the m-methyl, p-methyl, m-methoxy, and p-methoxyphenyl derivatives.     

Visible-light-promoted aerobic oxidative cyclization to access 1,3,4-oxadiazoles from aldehydes and acylhydrazides

A novel and practical access to symmetrical and unsymmetrical 2,5-disubstituted 1,3,4-oxadiazoles directly from aldehydes and acylhydrazides using visible light irradiation under an air atmosphere in the presence of eosin Y as an organophotoredox catalyst at rt is reported. This is the first example of oxidative cyclization of acylhydrazones employing air and visible light as inexpensive, readily available, non-toxic, and sustainable reagents.     

A remarkable cyclization of TADDOL-bisthioacetate under oxidative conditions

Abstract  

Attempted oxidation of a TADDOL-derived bisthioacetate resulted in a rather unexpected and remarkable cyclization and deprotection reaction, giving a thiolane-1,1-dioxide as the main product. Systematic in situ ESI-HRMS studies revealed a bicyclic, highly acid labile key intermediate of this reaction. Supported by force field calculations, the high sensitivity of this intermediate was judged to be due to the formation of a highly strained trans-configured bicyclo[3.3.0]skeleton.     

Synthesis of cis-solamin using a permanganate-mediated oxidative cyclization

[reaction: see text] cis-Solamin (1) and its diastereoisomer 14 have been synthesized in 13 steps using the diastereoselective permanganate-promoted oxidative cyclization of 1,5-dienes to create the tetrahydrofuran diol core. Notably, no protecting groups are required during the stages of fragment assembly.     

Green chemistry: solvent- and metal-free Prins cyclization. Application to sequential reactions

Prins cyclization between a homoallylic alcohol and an aldehyde, promoted by trimethylsilyl halide, afforded 4-halo-tetrahydropyrans with good to excellent yields. Thanks to the absence of the solvent and metal, the THP thus obtained have been implicated without purification in several other reactions, in a sequential way, affording in particular new indole derivatives.