Surprising 1,7-cyclization of vinyl carbonyl ylides generated from reaction of indanetrione with vinyl diazo compounds

Reactions of tricarbonyl compounds with vinyl diazo compounds 2 were carried out. Reaction of 1,2,3-indanetrione with 2a,b,c gave the spiroindan-1,3-dione-2,2′-benzodihydrooxepin 7a,b,c, but not normal products oxirane and dihydrofuran derivatives expected from intermediate vinyl carbonyl ylides 4. Formation of 7 requires isomerization of vinyl carbonyl ylides 4 bearing a (Z)-cyanostyryl group to unstable (E)-form 5 and subsequent cyclization to oxepin 6 followed by a 1,5-hydrogen shift. However, reaction of 2 with six-membered cyclic tricarbonyl compounds 1,2,3-trioxo-2,3-dihydrophenalene 11 and dimethylalloxane 13 gave the dioxole 12 and the dihydrofuran 14, respectively, typical products expected from vinyl carbonyl ylides.     

Synthesis of (S,Z)-3-[(1H-indol-3-yl)methylidene]hexahydropyrrolo[1,2-a]pyrazin-4(1H)-one: an alternative, enaminone based, route to unsaturated cyclodipeptides

A series of racemic and enantiopure (S,Z)-3-[(1H-indol-3-yl)methylidene]hexahydropyrrolo[1,2-a]pyrazin-4(1H)-one (cyclic Pro-ΔTrp) dipeptide analogues were prepared. Racemic analogues 6a-c were prepared by direct coupling of racemic cyclodipeptide enaminone (R,S)-5 with various indole derivatives. On the other hand, enantiopure analogues were prepared through a copper(I) catalyzed vinyl amidation reaction in which acyclic (S)-Pro-ΔTrp dipeptide analogues 20 and 21 were formed. Acyclic dipeptides were cyclized to enantiopure (S)-Pro-ΔTrp dipeptide analogues 24 and 25. For coupling reactions, vinyl bromides were prepared in several steps. From ethyl acetate (7), enaminone 8 was prepared and coupled with 2-methylindole and 2-phenylindole to give 9 and 10. Direct bromination of 3-(indole-3-yl)propenoates 9 and 10 at position 2 results in vinyl bromides 11 and 12. The Boc protecting group on the indole nitrogen 1′ in vinyl bromides 11 and 12 was introduced, before the copper(I) catalyzed coupling with N-Boc prolinamide 18 was performed. Enantiomeric purity of chiral intermediates and final products was determined mostly by HPLC or ¹H NMR spectroscopy and X-ray diffraction.     

[4+2] Cycloaddition reactions of 4-sulfur-substituted 2-pyridones with electron-deficient dienophiles

[4+2] Cycloaddition reactions of 4-(phenylthio)-1-tosyl-2-pyridone (6a) and 4-(phenylsulfonyl)-1-tosyl-2-pyridone (6b) with electron-deficient dienophiles 7 (N-methylmaleimide, N-phenylmaleimide, and methyl acrylate) gave new isoquinuclidine products 8-10. The N-tosyl group of 6a and 6b was also efficiently converted to N-alkyl derivatives 6c-f, which showed different stereoselectivity toward reactions with dienophiles 7. Several other dienophiles 15 (dimethyl acetylenedicarboxylate, methyl vinyl ketone, ethyl vinyl ether, and methyl methacrylate) were found not to react with 6a or 6b, but led to the formation of tosyl migration products 4-(phenylthio)-O-tosyl-pyridinol (16a) and 4-(phenylsulfonyl)-O-tosyl-2-pyridinol (16b), respectively. The reactivity, regioselectivity, and stereoselectivity of the cycloaddition reactions were also compared with semi-empirical calculations.     

A strategy towards the synthesis of plumarellide based on biosynthesis speculation,featuring a transannular 4+2 type cyclisation from a cembranoid furanoxonium ion intermediate

In studies towards a biomimetic synthesis of plumarellide 1, acid-catalysed rearrangement of the furanobutenolide-based acetonide 10b led to the ring system 15b in plumarellide together with the cycloheptene-based ring system 11 found in rameswaralide 4, in a combined yield of 60%. RCM of the ω-dienes 30a and 30b led to the macrocycles 38a and 38b, respectively with the Z-configuration. Treatment of the vinyl bromide/vinyl stannanes 32a and 47 under Stille conditions failed to give the macrocycles 31a and 48, respectively. Reactions of the macrocycles 38a and 38b with TFA containing water produced the 5,6,7-tricyclic compounds 56a and 56b, respectively in >90% yield, instead of the plumarellide-based ring system 52. A summary and perspective on possible pathways from the C-13 acetoxy furanocembranoid 66 and from the C13–C14 unsaturated enol ether/cyclic hemiketal 9/59 to plumarellide 1 in vivo is given.     

Unusual sulfanylation through ring transformation of arene-tethered 2H-pyran-2-ones by in situ built Michael adduct

A novel synthesis of highly functionalized alkylsulfanylmethyl arenes 8a-m through the ring transformation of 6-aryl-4-methyl/ethylsulfanyl-2H-pyran-2-one-3-carbonitriles 1a-j, by reaction with methyl vinyl ketone 2, is delineated and illustrated. To ascertain the course of reaction, 3-arylsulfanylmethyl-2-methyl-6-methylsulfanyl-4-phenylbenzonitriles 8k-m were also prepared from the reaction of 1 with 4-arylsulfanyl-butan-2-ones 7c,d.     

Formation of (vinyl-ferrocenyl)stibines involving β-elimination: Hypervalent Sb-N bonding

Unusual syntheses of vinyl substituted ferrocenylstibines viz. diphenyl(2-vinylferrocenyl) stibine (2) and iodo-(N,N-dimethylaminoethylferrocenyl)(2-vinylferrocenyl)stibine (4) involving β-elimination, are reported. Stibines Ph₂SbFc (1) or Fc₂SbCl (3) containing dimethylaminoethyl-pendant arm on a ferrocenyl ring on reaction with MeI gives vinyl substituted ferrocenylstibines. All the new stibines were characterized by IR, mass, ¹H, ¹³C, COSY, HETCOR NMR spectroscopy. The structures of all of these 1,2-disubstituted ferrocenylstibines were determined by X-ray diffraction analyses. The compounds 3 and 4 show hypervalent bonding between the antimony and nitrogen atoms giving 6 and 5 coordinated antimony, respectively. This is the first report on ferrocenylstibines containing a vinyl group in their framework.     

Syntheses of aza and fluorine-substituted 3-(piperidin-4-yl)-4,5-dihydro-1H-benzo[d][1,3]diazepin-2(3H)-ones

A practical and expedient synthesis of the title compounds is described. They were prepared by Stille reaction of nitro halopyridines 4 or nitro fluro-halobenzenes 10, followed by Michael addition of tert-butyl 4-aminopiperidine-1-carboxylate to the resulting activated vinyl compounds 5 and 11, hydrogenation (-NO₂→-NH₂), cyclic urea formation, Boc removal, and HCl salt formation. However, N3 and F1 analogs could not be made by this general strategy. Activated vinyl compounds 5a and 5d when reacted with tert-butyl 4-aminopiperidine-1-carboxylate did not stop at the desired Michael addition stage; but proceeded to produce azaindolines 8 and 9. Michael addition did not occur to compound 11d; instead, the fluorine atom was displaced.     

Studies on the Synthesis of Reidispongiolide A: Stereoselective Synthesis of the C(22)-C(36) Fragment

A highly stereoselective synthesis of the C(22)-C(36) fragment 2 of reidispongiolide A is described. This synthesis features the highly stereoselective mismatched double asymmetric crotylboration reaction of the aldehyde derived from 5 and the new chiral reagent (S)-(E)-7 that provides 12 with >15:1 dr. Subsequent coupling of the derived vinyl iodide 3 with aldehyde 16 provided allylic alcohol 17, that was elaborated by three steps into the targeted reidispongiolide fragment 2.     

Chemo enzymatic synthesis of Rengyol and Isorengyol

Cyanohydrins 2 of O-protected 4-hydroxycyclohexanones 1 are excellent starting compounds for the synthesis of Isorengyol (I) and Rengyol (II). The cyano group of the O-benzyl derivative 2d is first converted into the corresponding aldehyde 4, which via Wittig olefination led to the vinyl compound 6. Hydroboration of the trans-derivative (trans-6) leads, after debenzylation, to Isorengyol, whereas hydroboration and debenzylation of the cis-isomer (cis-6) gives Rengyol. With hydroxynitrile lyases (HNLs) as catalysts the stereoselective preparation of cis- as well as trans-cyanohydrin 2d is possible, which enables the selective preparation of Isorengyol or Rengyol, respectively. The trans-configuration of Isorengyol and the cis-configuration of Rengyol were secured by X-ray crystal structure analysis.     

Organometallic reagent-mediated one-pot synthesis of 3,5,6-trisubstituted naphthostyrils

A one-pot synthesis of 3,5,6-trisubstituted naphthostyrils is described. Addition of organometallic reagents to β-iodovinyl ketone 1 followed by elimination gave the Z-form β-alkyl vinyl ketone 15. Intramolecular cyclization of 15 under the reaction conditions afforded 3,5,6-trisubstituted naphthostyrils 4.     

Synthesis and phototransformations of novel styryl-substituted furo-benzobicyclo[3.2.1]octadiene derivatives

Novel cis- and trans-(o-H/Me/vinyl) substituted styryl furo-benzobicyclo[3.2.1]octadiene derivatives (7a,b, 8) were prepared and transformed to the novel naphthofuran derivatives of benzobicyclo[3.2.1]octadiene (6a,b) and novel phenanthrene-benzobicyclo[3.2.1]octadiene derivative (11) by photochemical electrocyclic ring closure in the presence of iodine and by intramolecular photoinduced [4+2] cycloaddition, respectively. These novel annelated bicyclo[3.2.1]octadiene derivatives (6a,b, 11) are especially interesting for their rigid methano-bridged junction of two aromatic units at defined geometrical arrangement and thereby as potentials for molecular clips.     

A new synthetic entry to the tricyclic skeleton of FR901483 by palladium-catalyzed cyclization of vinyl bromides with ketone enolates

A new synthetic entry to the FR901483 core is described. The Pd-mediated cyclization of amino-tethered vinyl halides and ketone enolates from the azaspiro[4.5]decan-8-ones 5 and 10 gives the functionalized 7,10a-methanoperhydropyrrolo[1,2-a]azocines 1 and 11, respectively.     

Imino Diels-Alder reaction of boronates: A new route to 3,4-dihydroquinolines

The synthesis of a series of 3,4-dihydroquinolines (3b-e, 3h and 3i) by Imino Diels-Alder reactions involving sulfolene and boronates 2a-j derived from Schiff bases is described. The reactions are regioselective leading to 4-substituted dihydroquinolines with a cis relative stereochemistry between the phenyl group on the boron atom and the vinyl substituent at position 4, as established by X-ray diffraction analyses of 3b, 3e, 3h and 3i.Boronates 2 containing substituents meta to the imino fragment lead to 4-ethenyl-dihydroquinolines while para substituted derivatives are more reactive and lead to 4-cyclohexenylquinolines 4 formed by a second Diels-Alder reaction with excess of butadiene. The results show that boronates derived from Schiff bases are electron deficient species that react with sulfolene providing a new route to 3,4-dihydroquinolines. Moreover, polarization of the imine bond activates these system toward cycloaddition.     

Synthesis of new bicyclic lactam peptidomimetics by ring-closing metathesis reactions

An efficient and versatile synthetic method for the preparation of new fused bicyclic lactams 3a and 3b is described. The spirane cyclopentane nucleus was easily installed by diallylation of the pyroglutamate derivative 18 followed by ring-closing metathesis (RCM). A more practical and stereoselective method for the allylation of the α-methoxy carbamate 21, involving the use of InCl₃ as a Lewis acid, was developed. In the crucial coupling reaction of the diastereomeric mixture of cis- and trans-pirrolidine derivatives 5a and 5b with N-Cbz vinyl phenylalanine only the cis isomer was found to react. An RCM reaction on the dipeptides 25a and 25b followed by catalytic hydrogenation, gave the final epimeric bicyclic lactams 3a and 3b. The same synthetic sequence on the model compound 7, lacking the spiro cyclopentane nucleus, is also reported.     

Reactions of ethyl triphenylphosphoranylideneacetate with fluorinated β-ketoaldehyde derivatives

The reactions of fluorinated β-ketoaldehyde derivatives: β-alkoxyvinyl polyfluoroalkyl ketones 1 and fluorinated β-ketoacetals 2 with ethyl triphenylphosphoranylideneacetate 3 are described. In the case of ketones 1 the result of the reaction is a mixture of products: fluorinated alkoxydienes 5 (Wittig reaction product) and polyfluoroacyl vinyl ylides 7 (Michael addition product). The reaction with fluorinated β-ketoacetals 2 leads to a mixture of E- and Z-isomers of polyfluoroalkyl acrylates 8 and 9, respectively. The influence of the nature of fluorinated substituent and solvent or other factors on the outcome of the reactions are discussed.     

The synthesis of 2,4-dienyl fluoroalkyl ketones by a tandem three-stage sequence of propargyl 2-fluoroalkylvinyl ether formation, Claisen rearrangement, and allene-to-conjugated diene isomerization

A tandem three stages process to a series of trifluoromethyl and halodifluoromethyl 2,4-unsaturated ketones 4a-c is described. This process started with the preparation of 2-fluoroalkyl substituted propargyl vinyl ether 3a-d by treatment of a mixture of individual ethyl α-per(poly)fluoroalkyl acetates 1a-d and propargyl alcohol 2 in CH₂Cl₂ with the mixed base (Na₂CO₃/TEA) at ambient temperature. When heated in toluene at 80°C, these ethers readily underwent a tandem propargyl-allenyl Claisen rearrangement and isomerization of the resultant 3,4-dienone to give 2,4-unsaturated fluoroalkyl ketones 4a-c (Z/E mixture). The reaction of ethyl α-per(poly)fluoroalkyl acetate 1 with 1-phenyl propargyl alcohol 5 in refluxing CH₂Cl₂ in the presence of the mixed base (Na₂CO₃/TEA) directly afforded the corresponding unsaturated fluoroalkyl ketone 6a-c in one pot. In the presence of NaH, the reaction of ethyl 3-halo-3-fluoroalkylacrylates 8a-b with 1,1-dimethyl propargyl alcohol 9 at −50°C to 0°C also gave the unsaturated fluoroalkyl ketones 10a-b in one pot. The difluorovinyl propargyl ether 11 produced by reduction of 2-bromodifluoromethyl substituted propargyl vinyl ether 3b rearranged in hot benzene to give the corresponding allene 12 bearing a gem-difluoromethylene group in the middle of the aliphatic chain.     

Synthesis of monofluorinated indolizines and their derivatives by the 1,3-dipolar reaction of N-ylides with fluorinated vinyl tosylates

Monofluorinated indolizines 4, benzo[d]indolizines 7 and 4H-pyrrolo[1,2-a]benzimidazoles 8 were synthesized in moderate yields by 1,3-dipolar reaction between fluorinated vinyl tosylates 2a and N-ylides of pyridinium, isoquinolinium and benzimidazolinium, generated in situ from their halides salts. When the same N-ylides were allowed to react with 2,3,3-trifluoro-1-propenyl tosylate 2b, the unexpected product formylated indolizines and their derivatives 9 were obtained. The reaction mechanism is also proposed.     

A new approach to 2,2-disubstituted 1-(methylsulfanyl)vinyl phosphonates via an intermediate thiocarbonyl ylide

The reaction of methyl (diethylphosphoryl)dithioformate (6) with diaryldiazomethanes 7a-d in THF at −60 °C to room temperature followed by desulfurization is shown to be a convenient method for the preparation of 2,2-disubstituted 1-(methylsulfanyl)vinyl phosphonates 8a-d. The analogous reactions with 2-diazoacenaphthen-1-one (7f) or 2-diazocamphor (7g) in refluxing THF yield selectively the corresponding (Z)- and (E)-vinyl phosphonates 8f and 8g, respectively. These products can be easily oxidized to the vinylsulfoxides 13 and vinylsulfones 14. On the other hand, methyl (diethylphosphoryl)dithioformate (6) and 2-diazo-1,2-diphenylethanone (7e) in boiling THF react to give the 1,3-oxathiole 12. All these reactions occur via an intermediate thiocarbonyl ylide 11 followed by 1,3-dipolar electrocyclization and sulfur extrusion or 1,5-dipolar electrocyclization.     

Synthesis and chemistry of tricyclic cyclopropene-tricyclo[3.2.2.0]nona-2(4),6-diene

The 1,2-bridged tricyclic cyclopropene, tricyclo[3.2.2.0^2,4]nona-2(4),6-diene (1), has been synthesized by the elimination of 2-bromo-4-chlorotricyclo[3.2.2.0^2,4]-non-6-ene (5). Cyclopropene 1 will undergo different isomerizations in ether solution and in neat conditions. Compound 1 rearranged to an anti-Bredt compound 4 via diradical mechanism in ether and tricyclic compound 6 via vinyl carbene mechanism in neat conditions. Compound 1 can be trapped with DPIBF at different temperatures yielding different results: the exo-endo adduct 2 (exo-addition from the view of the cyclopropene and endo-addition from the view of bicyclo[2.2.2]octene) is a sole product at 0°C by slowly addition of methyllithium, and the exo-endo adduct 2, endo-endo adduct 9, anti-Bredt adduct 3, and styrene 8 are isolated at ether refluxing temperature. Styrene 8 is proposed to be formed from endo-endo adduct 9 by diradical mechanism. The chemistry of exo-endo adduct 2 and endo-endo adduct 9 is as well studied. The exo-endo adduct 2 undergoes hydration in trifluoroacetic acid to generate 1,3-cis-diol 11 followed by eliminations of water and formaldehyde to give naphthalene 12. The endo-endo adduct 9 reacts with water in tetrahydrofuran-containing silica gel to yield 1,4-cis-diol 10. Both 9 and 10 react with trifluoroacetic acid to form trans-3-hydroxy trifluoroacetate 13. Compound 13 will undergo hydrolysis and isomerization to generate 1,3-cis-diol 11 in trifluoroacetic acid.     

Reactions of chelated η-pentadienyl iron complexes with nucleophiles

Ferracyclic (1-3-η³)pentadienyl complexes with electronically decoupled allyl and vinyl moieties were reacted with various heteroatom and carbon nucleophiles. Primary amines selectively attacked neutral (4-6-η³-pentadienyl)ferralactones 2 on the end of the allyl ligand to give 3-(endo-vinyl)-(4-6-η³-allyl)ferralactams 4 and by a similar reaction of the latter eventually 6-(exo-vinyl)-(4-6-η³-allyl)ferralactams 5. -like attack on the conjugated coplanar vinyl residue of 2 was not observed. The cationic η³-allyl complex 3 was attacked by nucleophiles either on the allylic terminus furnishing free (1Z, 3E)-dienes 8, or on the vinyl residue which is part of an activated Michael system to give η⁴-1,3-diene complexes 9. η⁴-1,3,5-Triene complex 10 was obtained with basic nucleophiles.