Enantiopure 1,4-diols and 1,4-aminoalcohols via stereoselective acyclic sulfoxide-sulfenate rearrangement

Treatment of acyclic α-hydroxy and α-tosylamino sulfinyl dienes with amines affords enantiopure 1,4-diol or 1,4-hydroxysulfonamide derivatives in good yields and diastereoselectivities. This one-pot procedure entails a conjugate addition that triggers a diastereoselective sulfoxide-sulfenate [2,3]-sigmatropic rearrangement.     

Studies on the deprotonation and subsequent [1,4]-Wittig rearrangement of α-benzyloxyallylsilanes

Upon exposure to s-BuLi, benzyloxyallylsilane undergoes an unusually rapid and efficient [1,4]-Wittig rearrangement. Herein we describe efforts aimed at trapping the intermediate α-carbanion with an electrophile prior to rearrangement. The results of these experiments indicate that α-deprotonation and bond reorganization are separate events. Findings herein further indicate that the future success of benzyloxyallylsilanes in [1,4]-Wittig rearrangements will likely hinge on the acidity of the benzylic protons.     

Thienoquinolizidinones. Synthesis and rearrangement into new piperidino[1,2-a][1,3] or [1,4]diazepinones fused to a thiophene ring

A convenient route to thienoquinolizidinones is described starting from ethyl pipecolinate and suitable halogenomethylthiophenes or 3-chloromethylbenzothiophene. The Schmidt reaction and the Beckmann rearrangement of oximes of these ketones led to piperidino[1,2-a][1,3] or [1,4]diarepines fused to a thiophene ring.     

Novel synthesis of pyridazino[4,5-b][1,4]oxazin-3,8-diones

A novel and effective synthesis of pyridazino[4,5-b][1,4]oxazin-3,8-diones via Smiles rearrangement is presented. Treatment of N-substituted 2-chloro(or hydroxy)acetamide, 2-tetrahydropyranyl-4-chloro-5-hydroxy(or chloro)pyridazin-3-one and cesium carbonate in refluxing acetonitrile was afforded the corresponding pyridazino[4,5-b][1,4]oxazin-3,8-diones in excellent yield.     

Stannous chloride-mediated reductive cyclization-rearrangement of nitroarenyl ketones

Cyclization products are produced in excellent yields from using standard reaction conditions for nitroarene reduction to aminoarene with SnCl2. Thus, 4-methyl-2-(2-nitrobenzyl)-2H-1,4-benzothiazin-3(4H)-one (2b) upon treatment with SnCl2 in ethanol did not produce the expected aniline derivative. Instead, 6-methyl-11a, 12-dihydro-6H-quino[3,2-b][1,4]benzothiazine (3) was produced in excellent yield, presumably via novel Sn (IV)-mediated amidine formation from the initial aniline reduction product. Under identical reaction conditions, 2-(2-nitrophenyl)-thiochroman-4-one (6) produces ethyl 5,11-dihydrodibenzo[b,e][1,4]thiazepin-11-ylacetate (7). A novel semipinacol rearrangement is proposed to account for this extensive skeletal rearrangement. Aniline derivative (14) (from 6 treated with FeSO4.7H2O) forms 12-ethoxy-11,12-dihydro-6H-6,12-methanodibenzo[b,f][1,5]thiazocine (15) upon treatment with SnCl2 in ethanol. Thiophene analogues of 6 and 14 (18 and 19, respectively) react similarly, forming the analogous thiazepine (20) and cyclic N,O-acetals (21), respectively.     

Novel bicyclo[2.2.2]octanyl-1,4-benzodiazepinones. Their syntheses and rearrangement to bicyclooct-2-enylbenzimidazoles

The synthesis of the novel bicyclo[2.2.2]octanyl[1,4]benzodiazepinone ring system (IV) and its facile acid catalysed rearrangement to the corresponding bicyclo[2.2.2]oct-2-enylbenzirnid-azole system (IX) is described.     

Selective [5,5]‐Sigmatropic Rearrangement by Assembly of Aryl Sulfoxides with Allyl Nitriles

Aromatic [5,5]‐sigmatropic rearrangement is an appealing protocol for accessing 1,4‐substituted arenes. However, such a protocol has not been well utilized in organic synthesis because of the difficulties in the synthesis of the substrates, selectivity issues, and limited substrate scope. Described herein is a new [5,5]‐sigmatropic reaction utilizing readily available aryl sulfoxides and allyl nitriles. This reaction features mild reaction conditions, high chemo‐ and regioselectivity, excellent functional‐group compatibility, and broad substrate scope. Computational studies suggest that the success of the reaction can be attributed to the selective electrophilic assembly of the rearrangement precursors, in which a linear ‐C=C=N‐ linkage favors [5,5]‐sigmatropic rearrangement over the competitive [3,3]‐sigmatropic rearrangement.     

1,5]-Anion relay/[2,3]-Wittig rearrangement of 3,3-bis(silyl) allyl enol ethers: synthesis of useful vinyl bis(silane) species

The [1,5]-anion relay/[2,3]-Wittig rearrangement of 3,3-bis(silyl) enol allyl ethers has been developed. This reaction provides an efficient method to synthesize versatile vinyl bissilanes, which can be transformed into trisubstituted vinylsilanes through a [1,4]-Brook rearrangement/alkylation protocol using a wide range of electrophiles.     

Covalent metal-organic networks: pyridines induce 2-dimensional oligomerization of (mu-OC6H4O)2Mpy2 (M = Ti, V, Zr)

Treatment of M(OiPr)4 (M = Ti, V) and [Zr(OEt)4]4 with excess 1,4-HOC6H4OH in THF afforded [M(OC6H4O)a(OC6H4OH)3.34-1.83a(OiPr)0.66-0.17a(THF)0.2]n (M = Ti, 1-Ti; V, 1-V, 0.91 < or = a < or = 1.82) and [Zr(1,4-OC6H4O)2-x(OEt)2x]n (1-Zr, x = 0.9). The combination of of 1-M (M = Ti, V, Zr) or M(OiPr)4 (M = Ti, V), excess 1,4- or 1,3-HOC6H4OH, and pyridine or 4-phenylpyridine at 100 degrees C for 1 d to 2 weeks afforded various 2-dimensional covalent metal-organic networks: [cis-M(mu 1,4-OC6H4O)2py2] infinity (2-M, M = Ti, Zr), [trans-M(mu 1,4-OC6H4O)2py2.py] infinity (3-M, M = Ti, V), solid solutions [trans-TixV1-x(mu 1,4-OC6H4O)2py2.py] infinity (3-TixV1-x, x approximately 0.4, 0.6, 0.9), [trans-M(mu 1,4-OC6H4O)2(4-Ph-py)2] infinity (4-M, M = Ti, V), [trans-Ti(mu 1,3-OC6H4O)2py2] infinity (5-Ti), and [trans-Ti(mu 1,3-OC6H4O)2(4-Ph-py)2] infinity (6-Ti). Single-crystal X-ray diffraction experiments confirmed the pleated sheet structure of 2-Ti, the flat sheet structure of 3-Ti, and the rippled sheet structures of 4-Ti, 5-Ti, and 6-Ti. Through protolytic quenching studies and by correspondence of powder XRD patterns with known titanium species, the remaining complexes were structurally assigned. With py or 4-Ph-py present, aggregation of titanium centers is disrupted, relegating the building block to the cis- or trans-(ArO)4Tipy2 core. The sheet structure types are determined by the size of the metal and the interpenetration of the layers, which occurs primarily through the pyridine residues and inhibits intercalation chemistry.     

Novel rearranged ions observed for

C-terminal rearrangement ions [b(n-1) + H2O] (where n refers to the total number of residues of peptides) are frequently observed for peptides which contain basic amino acid(s), especially arginine, at or near their N termini in low- and high-energy collision-induced dissociation or post-source decay (PSD) spectra. Here we report a novel rearrangement, associated with PSD for serine- or threonine-containing peptides that are susceptible to C-terminal rearrangement. Based on PSD analyses of serine- or threonine-containing bradykinin and its analogs, which have been ethyl-esterified or 18O labeled at their C termini, the [b(k) + H2O] (where k denotes the position adjacent to the left of the Ser/Thr residue) ion is generally thought to be formed by the transfer of the hydroxyl moiety of a serine or threonine residue to the carbonyl group of the residue to its left accompanied by the loss of the remaining C-terminal portion of the peptide. When the Ser/Thr is at or near the C terminus, the present [b(k) + H2O] ion could be formed via two pathways, i.e., the Ser/Thr-related rearrangement and the conventional C-terminal rearrangement, which has been clearly verified by 18O labeling at the C terminus. In addition, the ions which are formally designated as [y(m)b(l) + H2O], where y(m)b(l) denotes a b-type internal ion, are also briefly described.     

Studies in the claisen rearrangement. Part XII . Synthesis of benzofuro[3,2-c] [l]-6a,lla-dihydro-lla-methylbenzopyrans from 1,4-diaryloxy-2-butynes

Successful Claisen rearrangement of a number of 1,4-diaryloxy-2-butynes is reported. The products of such a rearrangement are the benzofuro[3,2-c]benzopyrans. This novel rearrangement offers a facile synthetic route to tetracyclic derivatives resembling the naturally occurring pterocarpans.     

Rationally designed, polymeric, extended metal-ciprofloxacin complexes

Reactions of the antimicrobial fluoroquinolone ciprofloxacin (cfH) with metal salts in the presence of aromatic polycarboxylate ligands or under basic conditions produce fourteen new metal-cfH complexes, namely, [Ba2(cf)2(1,4-bdc)(H2O)2] x H2O (1), [Sr6(cf)6(1,4-bdc)3(H2O)6] x 2H2O (2), [M2(cfH)2(bptc)(H2O)2] x 8H2O (M = Mn3 and Cd4), [M(cfH)(1,3-bdc)] (M = Mn5, Co6, and Zn7), [Zn2(cfH)4(1,4-bdc)](1,4-bdc) x 13H2O (8), [Ca(cfH)2(1,2-Hbdc)2] x 2H2O (9) and [M(cf)2] x 2.5H2O (M = Mn10, Co11, Zn12, Cd13, and Mg14) (1,4-bdc = 1,4-benzenedicarboxylate, bptc = 3,3',4,4'-benzophenonetetracarboxylate, 1,3-bdc = 1,3-benzenedicarboxylate, 1,2-bdc = 1,2-benzenedicarboxylate). Their structures were determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra, and thermogravimetric analyses. The structures of 1 and 2 consist of unique two-dimensional arm-shaped layers. Compounds 3 and 4 are isostructural and feature one-dimensional structures formed from the interconnection of [M2(cfH)2(H2O)2] dimers with bptc ligands. Compounds 5-7 are isostructural and contain double-chain-like ribbons constructed from [M2(cfH)2(CO2)2] dimers and 1,3-bdc. Compound 8 consists of a pair of [Zn(cfH)2]2+ fragments bridged by a 1,4-bdc into a dinuclear dumbbell structure. Compound 9 is a neutral monomeric complex. To the best of our knowledge, compounds 1-9 are the first examples of metal-quinolone complexes that contain aromatic polycarboxylate ligands. Compounds 10-14 are isostructural and exhibit interesting two-dimensional rhombic grids featuring large cavities with dimensions of 13.6x13.6 A. Up to now, polymeric extended metal-cfH complexes have never been reported.     

Olefination of α,α'-divinyl ketones through catalytic Meyer-Schuster rearrangement

The direct olefination of 1,4-dien-3-ones remains a synthetic challenge. A two-step protocol, employing acetylide addition followed by catalytic Meyer-Schuster rearrangement has been developed for the olefination of 1,4-pentadien-3-ones to afford [3]dendralenes. Many of the traditional methods for the Meyer-Schuster rearrangement of alkynyl carbinols are not suitable with these highly unsaturated substrates because of their acid sensitivity. Unexpected reactivity during attempted rearrangement, including Nazarov-type electrocyclizations, is presented, along with conditions to promote the Meyer-Schuster rearrangement of ethoxyacetylene adducts using catalytic VO(acac)(2).     

Tetracyclic systems: Synthesis of isoindolo[1,2-b]thieno-[2,3(3,2 or 3,4)-e][1,3]thiazocines and Isoindolo[2,1-a]thieno-[2,3(3,2 or 3,4)-f][1,4] and [1,5]diazocines

Cyclization of thioglycolic acids derivatives 3a-d gave isoindolo[1,2-b]thieno[2,3(3,2 or 3,4)-e][1,3]-thiazocines 4a-d . Isoindolo[2,1-a]thieno[2,3(3,2 or 3,4)-f][1,4] or [1,5]diazocines 10b or 11a-c were synthesized from Beckmann or Schmidt rearrangement of the ketones 7a-c .     

Diazabicycloalkanes with bridgehead nitrogen atoms. 28. Stevens rearrangement of benzodiazabicycloalkenes

Stevens rearrangement of the benzyl bromides of benzo[b]-1,4-diazabicyclo[2.2.2]octene and benzo[f]-1,5-diazabicyclo[3.2.2]-nonene occurs with expansion of the diazabicyclic fragments to form a mixture of stereoisomers. Both the ethylene and the trimethylene bridges participate in the rearrangement of the nonene.For Communication 27 see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 383–387, March, 1993.     

Electron impact mass spectral fragmentation of 2a,4-disubstituted 2-chloro/2,2-dichloro-2,2a,3,4-tetrahydro-1H-azeto[2,1-d][1,5]benzothia zepin-1-ones

The mass spectrometric behaviour of nine 2a,4-disubstituted 2-chloro/2,2-dichloro-2,2a,3,4-tetrahydro-1H-azeto[2,1-d][1,5]b enzothiazepin-1-ones has been studied with the aid of mass-analysed ion kinetic energy spectrometry and accurate mass measurements under electron impact ionization. All compounds show a tendency to eliminate a neutral chlorine atom, or a chloroketene, or neutral propene, or styrene or substituted styrene molecule, plus Cl and/or H (or Cl) atom(s), to yield [M-Cl]+ ions, 2,3-dihydro-1,5-benzothiazepine derivative ions, 4,5-dihydro-5H-1,5-benzothiazepin-4-one ions which can further lose CO to give 1,4-benzothiazine ions. Both molecular ions and [M-Cl]+ ions show a tendency to eliminate an ethyl or benzyl/substituted benzyl radical to produce 2,2a-dihydro-1H-azeto[2,1-c][1,4]benzothiazin-1-one ions. The [M-Cl]+ ions could undergo rearrangement to yield 2,2a-dihydro-1H-azeto[2,1-d][1,5]benzothiazepin-1-one ions, 2,2a,3,4-tetrahydro-1H-azeto[1,2-a]quinoline ions or 1,1a,2,3-tetrahydro-azirino[2,1-d][1,5]benzothiazepine ions by loss of an ethane or a benzene/substituted benzene, a SH radical or a CO molecule. The molecular ions could also undergo rearrangement reactions to form other small fragment ions.     

(−)-Sparteine-Mediated Asymmetric Cyclocarbolithiation of Alkenes Combined with a Stereospecific retro-[1,4]-Brook Rearrangement

A novel domino-type reaction sequence consisting of an enantioselective intramolecular carbolithiation of 6-phenylhex-5-enyl carbamates and a highly stereospecific retro-[1,4]-Brook rearrangement is reported. The carbocycles are formed with high enantiomeric (er >98 : 2) and diastereoisomer ratios (dr >99 : 1) in good yields (47 – 60%). On the basis of the absolute configuration of the cyclization products, a stereoretentive mechanism is proposed for the retro-[1,4]-Brook rearrangement.     

Contribution a l'etude de la transformation thermique des aldazines α-ethyleniques. nouvelle voie d'acces aux pyrazoles halogenes ou substitues par des groupements phenoxy,thiophenoxy et thioethoxy en 3(5)

Azines of β-halogen-, aryloxy-, alkylthio- and arylthio-substituted acroleines when heated gave pyrazole derivatives which may be hydrolysed very easily to give N-unsubstituted pyrazoles bearing in the 3(5) position halogen, ArO, RS or ArS groups. The observed heterocyclisation was compared with thermal decomposition of cinnamald azine for which an ionic mechanism had been previously proposed, whereas we show that the involved mechanism is an internal 1,4-addition and, according to the nature of the migrating group, a thermal [1,3] or [1,5] sigmatropic rearrangement.     

alpha-Substituted acylsilanes via a highly selective [1,4]-Wittig rearrangement of alpha-benzyloxyallylsilane

alpha-Benzyloxyallylsilane undergoes efficient [1,4]-Wittig rearrangement to generate an enolate intermediate that can be trapped with various electrophiles, thereby providing a new synthetic approach to substituted acylsilanes.     

[1,4]‐S‐ to O‐Silyl Migration: Multicomponent Synthesis of α‐Thioketones through Chemoselective Transformation of Esters to Ketones with Organolithium Reagents

A [1,4]‐S‐ to O‐silyl migration has been exploited to chemoselectively transform esters into ketones by using organolithium reagents, allowing multicomponent synthesis of α‐thioketones. Mechanistic studies reveal that this migration proceeds in an intramolecular manner and is more favorable than the corresponding [1,5]‐S‐ to O‐ and [1,3]‐C‐ to O‐silyl migrations. The resulting α‐thioketones are valuable building blocks for the synthesis of cyclic or multifunctionalized organosulfur compounds.