MASS SPECTRA OF SELECTED SULFONES SULFONE-SULFINATE REARRANGEMENT

Abstract

Mass spectra of three sulfones selected to reveal certain structural features were obtained and interpreted. The mass spectra of the two isomeric sulfones, benzyl methyl sulfone and methyl p-tolyl sulfone, were quite different. The spectra showed that rearrangement of sulfones to the isomeric sulfinates occurs under the influence of the electron impact and that the migration of the aryl group is preferred over migration of the alkyl group.     

Nouveaux Reactifs Precurseurs D'Olefines Trisubstituees E: Les Oxydes De Phosphine

Abstract

From NMR data, phosphine oxides 4 show similarity to Pylids and give E trisubstituted olefins from saturated and unsaturated aldehydes.     

Scandium(III) zeolites as new heterogeneous catalysts: [4+2]cyclocondensation of in situ generated aryl imines with alkenes

Scandium(III)-exchanged zeolite was used as heterogeneous ligand-free catalysts for the [4+2]cyclocondensation of amines and aldehydes with alkenes through the in situ formation of imines. Such catalysts offered a versatile, efficient, and highly regio- and stereoselective synthesis of tetrahydroquinoline derivatives. These catalysts exhibited a wide scope and compatibility with functional groups. They are very simple to use, easy to remove (by simple filtration), and they are recyclable (up to three times without loss of activity).     

Asymmetric Synthesis of Tetrahydroisoquinoline Derivatives through 1,3-Dipolar Cycloaddition of C,N-Cyclic Azomethine Imines with Allyl Alkyl Ketones

A [3 + 2] 1,3-Dipolar cycloaddition of C,N-cyclic azomethine imines with allyl alkyl ketones has been achieved. The reaction proceeds under mild conditions and tolerates a wide range of functional groups. An array of tetrahydroisoquinoline derivatives is generally constructed with good diastereoselectivities and enantioselectivities (up to >25:1 dr, >95% ee). Moreover, the absolute configuration of the product was previously determined by using the quantum electronic circular dichroism calculation and ECD spectrum method.     

X=Y=ZH Systems as potential 1,3-dipoles. Part 58: Cycloaddition route to chiral conformationally constrained (R)-pro-(S)-pro peptidomimetics

Imines of (1S,9S)-t-butyl-9-amino-octahydro-6,10-dioxo-6H-pyridazino[1,2-a][1,2]diazepine-1-carboxylate undergo thermal (toluene, 110°C) or LiBr-DBU catalysed (MeCN, room temperature) regio- and stereo-specific cycloaddition to a range of chiral dipolarophiles giving enantiopure spiro-cycloadducts in excellent yield. The reactions proceed via intermediate NH azomethine ylides and litho azomethine ylides, respectively and results in the multiplication of chiral centres from 2 (one of which is lost in the process) to 5.     

Nickel(II)‐Catalyzed Enantioselective 1,3‐Dipolar Cycloaddition of Azomethine Imines with Alkylidene Malonates

We demonstrated an asymmetric 1,3‐dipolar cycloaddition of azomethine betaines with alkylidene malonates by using a chiral N,N′‐dioxide–Ni^II complex as a catalyst. Both aromatic‐ and aliphatic‐substituted alkylidene malonates were found to be suitable for the reaction. A range of trans‐pyrazolone derivatives was exclusively obtained with excellent yields (up to 99 % yield) and good enantioselectivities (up to 97 % ee) under mild reaction conditions. The reaction could be carried out on a gram scale with the good results being maintained. Control experiments were performed to elucidate the specific diastereoselectivity of the reaction. The formation of single trans isomers was dominated by secondary orbital interactions between the ester groups of the dipolarophile and the azomethine imine. On the basis of the experimental results and previous reports, a possible catalytic model was assumed.     

Regioselective Synthesis of 5-Trifluoromethyl 1,2,4-Triazoles via [3 + 2]-Cycloaddition of Nitrile Imines with CF3CN

We herein describe a general approach to 5-trifluoromethyl 1,2,4-triazoles via the [3 + 2]-cycloaddition of nitrile imines generated in situ from hydrazonyl chloride with CF₃CN, utilizing 2,2,2-trifluoroacetaldehyde O-(aryl)oxime as the precursor of trifluoroacetonitrile. Various functional groups, including alkyl-substituted hydrazonyl chloride, were tolerated during cycloaddition. Furthermore, the gram-scale synthesis and common downstream transformations proved the potential synthetic relevance of this developed methodology.     

Reductive Elimination at Pb(II) Center of an (Amino)plumbylene-Substituted Phosphaketene: New Pathway for Phosphinidene Synthesis

A stable (amino)plumbylene-substituted phosphaketene 3 was synthesized by the successive reactions of PbCl₂ with two anionic reagents (lithium amidophosphine and NaPCO). Of particular interest, the thermal evolution of 3 , at 80 °C, leads to the transient formation of corresponding amino- and phosphanylidene-phosphaketenes ( 6 and 7 ), via a reductive elimination at the Pb^II center forming new N−P and P−P bonds. Further evolution of 6 gives a new cyclic (amino)phosphanylidene phosphorane 4 , which shows a unique reactivity as a phosphinidene. This result provides a new synthetic route to phosphinidenes, extending and facilitating further their access.     

Metal‐Free,Regioselective Triazole Ligations that Deliver Locked cis Peptide Mimetics

Metal‐free triazole turns : 1,5‐Disubstituted peptidyl triazoles are obtained regioselectively from the 1,3‐dipolar cycloaddition of peptidyl phosphoranes and azides. Peptide turns are thus formed that contain a conformationally locked cis peptide bond. Being regioselective and free of heavy metals, this reaction may find broad application in chemical biology and medicinal chemistry.

     

Facile Synthesis of Tricyclic 1,2,4-Oxadiazolines-Fused Tetrahydro-Isoquinolines from Oxime Chlorides with 3,4-Dihydroisoquinoline Imines

A mild and efficient strategy for the synthesis of tricyclic 1,2,4-oxadiazolines-fused tetrahydro-isoquinolines derivatives via [3 + 2] cycloaddition reaction is reported. The reactions provided the functionalized tricyclic 1,2,4-oxadiazolines in high yields (up to 96%). This protocol is simple and easy to handle. Moreover, a gram-scale experiment further highlights the synthetic utility. The chemical structure of the product was determined by X-ray single-crystal structure analysis. A possible mechanism for this transformation is proposed to explain the reaction process.     

Radical Mediated Aza‐Pauson‐Khand Reaction of Acetylenes,Imines, and CO Leading to Five‐Membered Unsaturated Lactams

Formal [2+2+1] cycloaddition reaction involving acetylenes, aromatic imines, and CO was achieved by radical chain reaction, which gave five‐membered unsaturated lactams in modest to good yields. When we used 5‐chloropentyne, sequential carbonylation took place accompanied with double annulation events to give a cyclohexanone‐fused lactam in excellent stereoselectivity.     

Umpolung of Imines Enables Catalytic Asymmetric Regio‐reversed [3+2] Cycloadditions of Iminoesters with Nitroolefins

A copper‐catalyzed regio‐reversed asymmetric [3+2] cycloaddition of iminoesters with nitroolefins is disclosed for the first time. This method enables the facile synthesis of polysubstituted chiral pyrrolidines bearing at least one chiral quaternary center in high yields with excellent regio‐, diastereo‐, and enantioselectivity. The application of chiral P,S ligands and the unique effect of α‐aryl groups on the iminoesters are key to the success of this method. The practicality and versatility of the reaction are also demonstrated.