Iodine-alumina as an efficient and useful catalyst for the regeneration of carbonyl functionality from the corresponding 1,3-oxathiolanes and 1,3-dithiolanes in aqueous system

A simple and useful method has been demonstrated for the deprotection of 1,3-oxathiolanes and 1,3-dithiolanes to the corresponding carbonyl compounds in excellent yield by employing catalytic amount (30 mol %) of iodine supported on neutral alumina in ethanol-water or water. The major advantages of this protocol are mild reaction conditions, less reaction time, easy to handle, high yields, inexpensive reagent and environmentally benign.     

Synthesis of some 2-ylidene-1,3-dithiolanes

Russian Journal of Organic Chemistry - Convenient procedures have been developed for the synthesis of 2-(1,3-dithiolan-2-ylidene)- malononitriles and 2-cyano-2-(1,3-dithiolan-2-ylidene)acetamides...     

One-Pot Synthesis of 2-Ylidene-1,3-dithiolanes

Russian Journal of Organic Chemistry - A one-pot synthesis of 2-ylidene-1,3-dithiolanes, involving the reaction of carbon disulfide with methylene-active compounds in the presence of sodium...     

Electron impact induced fragmentations of some 2,2-disubstituted 1,3-dithiolanes

Electron impact induced fragmentations of the title compounds were studied by exact mass measurement and metastable ion analysis. Sulphur atoms within the ring effectively stabilize the positive charge. In most cases the loss of the larger substituent, and not the other, methyl group, gives rise to the base peak in the spectrum. Examination of competing metastable transitions shows that generally this is also the lowest activation energy primary process. In general primary ring cleavage reactions are not important unless there is a heteroatom in the substituent that can assist this cleavage.     

Water mediated synthesis of various [1,3]oxazine compounds using alum as a catalyst

Abstract

A simple, efficient, and practical procedure for the synthesis of various substituted 2,3-dihydro-2-phenyl-1H-naphtho[1,2-e][1,3]oxazines and 3,4-dihydro-3-phenyl-2H-naphtho[2,1-e][1,3]oxazines using KAl(SO₄)₂ 12H₂O (alum) as a non-toxic, reusable, inexpensive, and easily available catalyst is described using water as a solvent. These improved reaction conditions allow the preparation of a wide variety of substituted [1,3]oxazines in high yields and purity under mild reaction conditions.     

Asymmetric allylation of unsymmetrical 1,3-diketones using a BINAP-palladium catalyst

[reaction: see text] The chiral palladium complex generated in situ from [Pd(eta(3)-allyl)Cl](2) and (R)-BINAP is a good catalyst for the catalytic asymmetric allylation of 1,3-diketones. The reaction provided chiral 2,2-dialkyl-1,3-diketones with 64-89% ee in high yields (13 examples). Enantiomeric excesses are strongly affected by the gamma-substituent of the allylic substrates. A variety of unsymmetrical 1,3-diketones were alkylated with cinnamyl acetate in good enantioselectivities via use of the BINAP-palladium catalyst (77-89% ee).     

Reactions on solid supports part II: a convenient method for synthesis of pyrromethanes using a montmorillonite clay as catalyst

α-Acetoxymethylpyrroles couple with α-free pyrroles in presence of Montmorillonite clay to form unsymmetrical pyrromethanes in excellent yields. Symmetrical pyrromethanes were also prepared in a similar manner by clay catalysed self-condensation of α-acetoxymethylpyrroles.     

Cationic cyclization of 2-alkenyl-1,3-dithiolanes: diastereoselective synthesis of trans-decalins

An unprecedented and highly diastereoselective 6-endo-trig cyclization of 2-alkenyl-1,3-dithiolanes has been developed yielding trans-decalins, an important scaffold present in numerous di- and triterpenes. The novelty of this 6-endo-trig cyclization stands in the stepwise mechanism involving 2-alkenyl-1,3-dithiolane, acting as a novel latent initiator. It is suggested that the thioketal opens temporarily under the influence of TMSOTf, triggering the cationic 6-endo-trig cyclization, and closes after C-C bond formation and diastereoselective protonation to terminate the process. DFT calculations confirm this mechanistic proposal and provide a rationale for the observed diastereoselectivity. The reaction tolerates a wide range of functionalities and nucleophilic partners within the substrate. We have also shown that the one-pot 6-endo-trig cyclization followed by in situ 1,3-dithiolane deprotection afford directly the corresponding ketone. This improvement allowed the achievement of the shortest total synthesis of triptophenolide and the shortest formal synthesis of triptolide.     

Synthesis of 2-phenyl pyridine derivatives from aryl ketones and 1,3-diaminopropane using palladium acetate as a catalyst

A simple and efficient method for the synthesis of 2-phenyl pyridine via cyclization of aryl ketone with 1,3-diaminopropane using palladium acetate is established. This method is mild, operationally simple, involves short reaction time and involves easy workup procedure to afford the corresponding 2-phenyl pyridines in moderate to good yield.     

gem-Difluorination of 2,2-diaryl-1,3-dithiolanes by Selectfluor and pyridinium polyhydrogen fluoride

2,2-diaryl-1,3-dithiolanes, readily obtainable from diaryl ketones, were transformed into the corresponding gem-difluoro compounds using a novel reagent combination involving Selectfluor and pyridinium polyhydrogen fluoride (PPHF) under mild conditions in moderate to good yields.     

Pickering miniemulsion polymerization using Laponite clay as a stabilizer

Solid-stabilized, or Pickering, miniemulsion polymerizations using Laponite clay discs as stabilizer are investigated. Free radical polymerizations are carried out using a variety of hydrophobic monomers (i.e., styrene, lauryl (meth)acrylate, butyl (meth)acrylate, octyl acrylate, and 2-ethyl hexyl acrylate). Armored latexes, of which the surfaces of the particles are covered with clay discs, are obtained, as confirmed by scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). Overall polymerization kinetics of the Pickering miniemulsion polymerizations of styrene were investigated via gravimetry. Comparison with the bulk polymerization analogue clearly shows compartmentalization. Moreover, retardation effects up to intermediate monomer conversions are observed; they are more prominent for the smaller particles and are ascribed to the Laponite clay. A model is presented that allows for the prediction of the average particle size of the latexes produced as a function of the amounts of monomer and Pickering stabilizers used. It shows that under specific generic conditions the number of clay discs used correlates in a linear fashion with the total surface area of the latex particles. This is a direct result of the reversibility of the Laponite clay disc adhesion process under the emulsification conditions (i.e., sonication) used.     

Facile redbrick clay as splendid catalyst for selective dehydration of alcohols

Research on Chemical Intermediates - Excellent catalytic activity of activated redbrick clay (ARB) for dehydration and highly selective conversion of cyclohexanol to cyclohexene and 1-phenylethanol...     

Electron-impact studies—XLVII: The mass spectra of 2-aryl-1,3-dithianes and -1,3-dithiolanes

The fragmentation patterns in the spectra of 2-aryl-1,3-dithianes and -1,3-dithiolanes have been elucidated by deuterium labelling studies. Ortho effects are observed in the spectra of 2(o-alkoxyphenyl)-1,3-dithianes. The molecular ions of the 1,3-dithianes eliminate S2H· and metastable kpeaks substantiate these eliminations. The hydrogen involved in this elimination randomises (C-4, 5 and 6) Prior to elimination in the spectrum of 2-phenyl-1,3-dithiane, but originates mainly from C-5 in that of the bis propane-1,3-dithioacetal of terephthaldehyde.     

Iodine as a versatile catalyst for the hydroalkylation of vinyl arenes with 1,3-diketones

The vinyl arenes undergo smooth hydroalkylation with 1,3-diketones in the presence of 10 mol % of iodine to afford phenethyl diketones and ketoesters in good yields in short reaction times. The use of inexpensive and readily available molecular iodine makes this method quite simple, more convenient and practical.     

Simple and efficient deprotection of 1,3-dithianes and 1,3-dithiolanes by copper(II) salts under solvent-free conditions

Aerobic solid state deprotection of 1,3-dithianes and 1,3-dithiolanes of aromatic and aliphatic aldehydes and ketones has been performed in excellent yields by Cu(NO₃)₂·2.5H₂O in the presence of montmorillonite K10 clay and sonic waves at room temperature. These dethioacetalizations proceed more slowly but efficiently under catalytic conditions by using 20% of the copper(II) salt with K10 clay and sonication.     

1,3-dithiolanes from cycloadditions of alicyclic and aliphatic thiocarbonyl ylides with thiones: regioselectivity

The regiochemistry of 1,3-dithiolanes obtained from thiocarbonyl ylides 9 and thiones 10 shows a striking dependence on substituents. Previously and newly performed experiments indicate that sterically hindered cycloalkanethione S-methylides and dialkylthioketone S-methylides react with alicyclic and aliphatic thiones to give the 2,2,4,4-tetrasubstituted 1,3-dithiolanes 11 exclusively. Aryl groups in one or both reactants lead to a preference for, or even complete formation of, 4,4,5,5-tetrasubstituted 1,3-dithiolanes 12. Several mechanisms appear to be involved, but the paucity of experimental criteria is troubling. Quantum-chemical calculations (see preceding paper) on the cycloaddition between thioacetone S-methylide and thioacetone furnish lower activation energies for the concerted process than for the two-step pathways via C,S- or C,C-biradicals; the favoring of the 2,4-substituted 1,3-dithiolanes over the 4,5-substituted type would be expected to increase with growing bulk of substituents. Aryl groups stabilize intermediate biradicals. Experimental criteria for the differentiation of regioisomeric dithiolanes are discussed. Thiocarbonyl ylides 9 are prepared by 1,3-cycloadditions between diazomethane and thioketones and subsequent N(2) elimination from the usually isolable 2,5-dihydro-1,3,4-thiadiazoles 17; different ratios of the two rate constants lead to divergent product formation scenarios.