Preparation and characterization of 6-substituted 1,8-diazabicyclo[5.4.0]undec-7-ene

The lithium 1,8-diazabicyclo[5.4.0]undec-6-ide ( 1 ) prepared from 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and n-butyllithium reacts with alkyl halides and carbonyl compounds such as benzophenone, acetophenone, and benzaldehyde to give 6-substituted DBU derivatives in good yields. The reaction behavior of 6-substi-tuted DBU was also investigated.     

Reactions of Nucleosides with 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU). Syntheses of N(3)-Methylene-Bridged Bis-uridines and Secouridine-Dinucleoside Analogs

Diasteroisomeric secouridine derivatives, appropriately protected and activated, served as starting compounds in the reactions with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in various solvents (CH₂Cl₂, MeCN, or dimethylformamide (DMF)). Reactions with DBU/CH₂Cl₂ gave N(3)-methylene-bridged bis-secouridines and bis-uridines (Scheme 3), while the reactions with DBU in non-alkylating solvents resulted in formation of secdinucleosides as the result of intermolecular ‘dimerizations’ (Scheme 2).     

Unerwartete Reduktion von [Cp*TaCl4(PH2R)] (R = But,Cy, Ad,Ph, 2,4,6‐Me3C6H2; Cp* = C5Me5) durch Reaktion mit DBU – Molekülstruktur von [(DBU)H][Cp*TaCl4] (DBU = 1,8‐Diazabicyclo[5.4.0]undec‐7‐en)

Unexpected Reduction of [Cp*TaCl₄(PH₂R)] (R = Bu^t, Cy, Ad, Ph, 2,4,6‐Me₃C₆H₂; Cp* = C₅Me₅) by Reaction with DBU – Molecular Structure of [(DBU)H][Cp*TaCl₄] (DBU = 1,8‐diazabicyclo[5.4.0]undec‐7‐ene) [Cp*TaCl₄(PH₂R)] (R = Bu^t, Cy, Ad, Ph, 2,4,6‐Me₃C₆H₂ (Mes); Cp* = C₅Me₅) react with DBU in an internal redox reaction with formation of [(DBU)H][Cp*TaCl₄] ( 1 ) (DBU = 1,8‐diazabicyclo[5.4.0]undec‐7‐ene) and the corresponding diphosphane (P₂H₂R₂) or decomposition products thereof. 1 was characterised spectroscopically and by crystal structure determination. In the solid state, hydrogen bonding between the (DBU)H cation and one chloro ligand of the anion is observed.     

Synthesis of 3-Trifluoromethyl-Substituted Benzo[f]chromene Derivatives in a One-Pot Reaction

In the presence of 1,8-diazabicycolo[5.4.0]undec-7-ene (DBU) and concentrated H₂SO₄, 2-naphthol reacted smoothly with α,β-unsaturated trifluoromethyl ketones in CH₂Cl₂ at room temperature, affording the 3-trifluoromethyl-substituted benzo[f]chromene derivatives in good to excellent yields in a one-pot reaction.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource: Full experimental and spectral details].     

Sonochemical fluorination of heterocyclic nitro compounds with Selectfluor™ (F-TEDA-BF4)

CH and CH₂ groups attached to a heterocycle and a nitro function were rapidly mono- or difluorinated by reaction with 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2,2,2]octane bis-tetrafluoroborate (Selectfluor) in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), preferably with ultrasonic irradiation.     

Total Synthesis of (±)-Gelsemine

A complex molecular reorganization ( 1 → 2 ), a sequential anionic aza-Cope rearrangement and Mannich cyclization, and an unprecedented intramolecular Heck reaction of the tetrasubstituted double bond of a vinylogous carbamate are key steps in a new total synthesis of (±)-gelsemine ( 3 ). MOM=methoxymethyl, DBU=1,8-diazabicyclo[5.4.0]undec-7-ene.     

Dehydroiodination of 2-iodo-3-(polyfluoroalkyl)propoxymethyloxiranes

Dehydroiodination of 2-iodo-3-(polyfluoroalkyl)propoxymethyloxiranes upon treatment with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) afforded (polyfluoroalk-2-enyl)oxymethyloxiranes as E-and Z-isomers in ratio depending on the nature of the fluoroalkyl substituent. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2160–2162, November, 2007.     

Unexpected cis-Selective 1,4-Addition Reaction of Lower Order Cyanocuprates to Optically Active 5-(tert-Butyldimethylsiloxy)-2-cyclohexenone

A remarkable cis selectivity has been observed in the 1,4-addition of lower order primary and secondary alkylcyanocuprates to 5-silyloxy- and 5-benzyloxy-substituted cyclohexenones. This enables the preparation of both enantiomers of the corresponding 5-alkyl-substituted cyclohexenones (S)- and (R)- 3 by the reaction of the readily available 5-(tert-butyldimethylsiloxy)-2-cyclohexenone ( 1 ) with either the lower or higher order cyanocuprate. DBU=1,8-diazabicyclo[5.4.0]undec-7-ene.     

Novel transformations of two kinds of chlorinated photo [2 + 2] cycloadducts of 2-pyrone-5-carboxylate

Novel reactions of 7,7-dichloro- and 7,7,8-trichloro-3-oxo-2-oxabicyclo[4.2.0]oct-4-ene-6-carboxylates 5 with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in alcohol gave pyrano[4,3-b]pyran-2,5-diones 8 via (Z)-(2H-pyran-2-on-3-yl)butenoates 7. On the other hand, the same treatment of 7,7,8-trichloro-2-oxo-3-oxabicyclo-[4.2.0]oct-4-ene-5-carboxylate 6b afforded 2-oxo-3-oxabicyclo[4.2.0]oct-4,7-diene-5-carboxylate 14 via cyclobutene formation and S_N2′ displacement by attack of the alkoxy anion.     

Synthesis and spectrophotometric study of the acid-base and complexing properties of 2,3,7,8,12,13,17,18-Octaethyl-5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin in acetonitrile

2,3,7,8,12,13,17,18-Octaethyl-5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin has been synthesized, and its acid-base and complexing properties in the systems 1,8-diazabicyclo[5.4.0]undec-7-ene-acetonitrile, acetonitrile-Zn(OAc)₂, and 1,8-diazabicyclo[5.4.0]undec-7-ene-acetonitrile-Zn(OAc)₂ have been studied by spectrophotometry. Titration of 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin with 1,8-diazabicyclo[5.4.0]undec-7-ene is accompanied by successive deprotonation of the pyrrole nitrogen atoms with formation of the corresponding mono- and dianion. The overall acid dissociation constant of the title compound has been determined. The complexation of neutral and doubly deprotonated 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin with Zn(OAc)₂ has been studied, and kinetic parameters for the formation of the zinc complex according to the molecular and ionic mechanisms have been determined. Extra coordination of 1,8-diazabicyclo[5.4.0]undec-7-ene by the zinc complex of 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin.     

Instructions to Authors (1994)

(1S,2R,6R,7R)-4-Phenyl-3,10-dioxa-5-azatricyclo[5.2.1.0^2,6]dec-4-en-9-one ((+)- 5 ) obtained in 6 steps from the Diels-Alder adduct of furan to 1-cyanovinyl (1S)-camphanate ((+)- 3 ) was reduced to the corresponding endo-alcohol (?)- 6 the treatment of which with HBr/AcOH provided (?)-(3aS,4S,6R,7S,7aR)-4β-bromo-3aβ,4,5,6,7,7aβ-hexahydro-2-phenyl-1,3-benzoxazole-6β,7α-diyl diacetate ((?)- 17 ). Elimination of HBr with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and acidic hydrolysis furnished (?)-(1R,2S,3R,4R)-4-aminocyclohex-5-ene-1,2,3-triol ( ? (?)-conduramine C₁;(?)- 1 ).     

The simple solvent-free synthesis of 1H-quinazoline-2,4-diones using supercritical carbon dioxide and catalytic amount of base

Only supercritical carbon dioxide (scCO₂) as a reactant and a solvent, and catalytic amount of base (DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), DBN (1,5-diazabicyclo[4.3.0]non-5-ene), Dabco^® (1,4-diazabicyclo[2.2.2]octane), and triethylamine) afforded 1H-quinazoline-2,4-diones in good to excellent yields from 2-aminobenzonitriles. 6,7-Dimethoxy-1H-quinazoline-2,4-dione, which is a key intermediate of medicines (Prazosin, Bunazosin, and Doxazosin) was synthesized successfully in a 97% yield, using 0.1 equiv of DBU under scCO₂ (10 MPa) at 80 °C.     

Syntheses and Structures of Two Selenite Chloride Hydrates: Co(HSeO3)Cl · 3 H2O and Cu(HSeO3)Cl · 2 H2O

The first selenite chloride hydrates, Co(HSeO₃)Cl · 3 H₂O and Cu(HSeO₃)Cl · 2 H₂O, have been prepared from solution and characterised by single‐crystal X‐ray diffraction. The cobalt phase adopts an unusual “one‐dimensional” structure built up from vertex‐sharing pyramidal [HSeO₃]^2–, and octahedral [CoO₂(H₂O)₄]^2– and [CoO₂(H₂O)₂Cl₂]^4– units. Inter‐chain bonding is by way of hydrogen bonds or van der Waals' interactions. The atomic arrangement of the copper phase involves [HSeO₃]^2– pyramids and Jahn‐Teller distorted [CuCl₂(H₂O)₄] and [CuO₄Cl₂]^8– octahedra, sharing vertices by way of Cu–O–Se and Cu–Cl–Cu bonds. Crystal data: Co(HSeO₃)Cl · 3 H₂O, M_r = 276.40, triclinic, space group P 1 (No. 2), a = 7.1657(5) Å, b = 7.3714(5) Å, c = 7.7064(5) Å, α = 64.934(1)°, β = 68.894(1)°, γ = 71.795(1)°, V = 337.78(7) ų, Z = 2, R(F) = 0.036, wR(F) = 0.049. Cu(HSeO₃)Cl · 2 H₂O, M_r = 263.00, orthorhombic, space group Pnma (No. 62), a = 9.1488(3) Å, b = 17.8351(7) Å, c = 7.2293(3) Å, V = 1179.6(2) ų, Z = 8, R(F) = 0.021, wR(F) = 0.024.     

1,8-Diazabicyclo[5.4.0]undec-7-ene as a ligand in an intermediate in selective carbonyl substitution of a ruthenium-cobalt complex

1,8-Diazabicyclo[5.4.0]undec-7-ene, DBU, reacts with (OC)₄Ru(μ-PPh₂)Co(CO)₃ (1) at room temperature to give an intermediate 2, which on protonation in the presence of Co regenerates 1 and on protonation in the presence of PMe₃, gives the monosubstituted product (OC)₃(L)Ru(μ-PPh₂)Co(CO)₃ (3 L = PMe₃). DBU promotes the selective formation of 4(L = PPh₂Me) or 5 (L = Ph₂PCh₂C(Me)CH₂) in one-step from 1, Ph₂PH, and methyl iodide or methallyl chloride, respectively.     

Transesterifications with 1,8-Diazabicyclo[5.4.0]undec-7-ene/Lithium Bromide (DBU/LiBr) – Also Applicable to Cleavage of Peptides from Resins in Merrifleld Syntheses

A mixture of the amidine base 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and LiBr (preferably 0,5 and 5 equiv., resp.) turns out to be a highly efficient catalyst (at 0–25°) for saponifications (in THF/H₂O) and transesterifications (in ROH). The scope and limitations of the method are determined using ca. two dozens of different ester/alcohol combinations (Schemes 2 and 3). The investigation is focused on peptides as substrates. Under carefully controlled conditions, no epirnerization occurs with N-Boc- and N-Z-protected peptide esters, when methyl, ethyl, isopropyl, or allyl esters are the products, as shown for peptides containing up to six amino acids, with Ala, Len MeLeu, Asp(OEt), or Tyr at the C-terminus (Scheme 3 and Tables 1 and 2). Hydrolytic and transesterifying detachments of Boc-Leu-Ala-Gly-Val-OR and Boc-Leu-Ala-Gly-Phe-OR (R = H, Me) from PAM and Wang resins (1–8 h at 0–25°, 2 equiv. of DBU, 5 equiv. of LiBr) can be achieved by this method without epimerization of the C-terrninal stereogenic center; a comparison with other methods (HF, Ti(OR)₄) is given (Schemes 4 and 5). Possible protecting-group strategies involving the DBU/LiBr method are discussed (Table 3), Extensive experimental details are given.     

Synthesis of alkenyl 3-hydroxy-2-naphthoates

Esterification of 3-hydroxy-2-naphthoic acid with homologous primary and secondary alkenyl alcohols with different chain lengths in the presence of N,N'-carbonyldiimidazole (CDI) and 1,8-diazabicyclo[ 5.4.0]undec-7-ene (DBU) in N,N-dimethylformamide gave the corresponding esters.     

On the reactions of aroylacetonitriles with acetoacetates

2,7-Diaryl-3-cyano-4-methylpyrano[4,3-b]pyridin-5-ones were synthesized by Ni(acac)₂-catalyzed condensation of aroylacetonitriles with acetoacetates. The competitive Knoevenagel reaction gave 6-aryl-5-cyano-4-methylpyran-2-ones as by-products. A preparative method for the synthesis of the latter compounds in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a catalyst was proposed.     

Oxacalix[3]arene complexes with the ReI(CO)3 fragment

Oxacalix[3]arenes p-methyloxacalix[3]arene (L(1)), p-isopropyloxacalix[3]arene (L2), and p-ethoxycarbonyloxacalix[3]arene (L3) are able to bind the Re(I)(CO)3 moiety with two of their three phenol-O atoms and one of their ether-O atoms. The monoanionic complexes were isolated in the salts (DBUH)[Re(CO)3(L1H-2)].L1 (1) and (NEt4)[Re(CO)3(L2H-2)].L2.0.5 MeCN (2) (DBU = 1,8-diazabicyclo[5.4.0]undec-7-ene). Over the course of its reaction with (NEt4)(2)[Re(CO)3Br(3)] and DBU, p-ethoxycarbonyloxacalix[3]arene decomposes to form [{Re(CO)3(L4H-2)}2] (3) {L4 = 1-(5-ethoxycarbonyl-2-hydroxy-3-hydroxymethyl-benzyl)-2,3,4,6,7,8,9,10-octahydro-pyrimido[1,2-a]azepin-1-ium. The expected monoanion [Re(CO)3(L3H-2)]- (4) was identified by 13C NMR and mass spectra.     

Palladium-catalysed dimerization of isoprene with carbon dioxide in the presence of organotin ethoxide and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)

The palladium-catalysed dimerization of isoprene with carbon dioxide is promoted by treatment wiht tributyltin ethoxide and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU).     

Unprecedented two-step synthesis of symmetrical diarylamines from 2-alkyl-1,3-dinitropropanes

This letter reports a new, two-step synthesis of symmetrical diarylamines from 1,3-dinitropropanes, by their reaction with acrolein under basic conditions (Al₂O₃, neat), followed by aromatisation of the obtained 2,4-dinitrocyclohexanols, through their treatment with four equivalents of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), in acetonitrile as a solvent, and warming overnight at 60 °C.