Synthesis, structure, and catalytic activity of titanium(IV) and zirconium(IV) amides with chiral biphenyldiamine-based ligands

A new series of titanium(IV) and zirconium(IV) amides have been prepared from the reaction between M(NMe₂)₄ (M = Ti, Zr) and C₂-symmetric ligands, (R)-2,2′-bis(pyridin-2-ylmethylamino)-6,6′-dimethyl-1,1′-biphenyl (2H₂), (R)-2,2′-bis(pyrrol-2-ylmethyleneamino)-6,6′-dimethyl-1,1′-biphenyl (3H₂), (R)-2,2′-bis(diphenylphosphinoylamino)-6,6′-dimethyl-1,1′-biphenyl (4H₂), (R)-2,2′-bis(methanesulphonylamino)-6,6′-dimethyl-1,1′-biphenyl (5H₂), (R)-2,2′-bis(p-toluenesulphonylamino)-6,6′-dimethyl-1,1′-biphenyl (6H₂), and C₁-symmetric ligands, (R)-2-(diphenylthiophosphoramino)-2′-(dimethylamino)-6,6′-dimethyl-1,1′-biphenyl (7H) and (R)-2-(pyridin-2-ylamino)-2′-(dimethylamino)-6,6′-dimethyl-1,1′-biphenyl (8H), which are derived from (R)-2,2′-diamino-6,6′-dimethyl-1,1′-biphenyl. Treatment of M(NMe₂)₄ with 1 equiv. of N₄-ligand, 2H₂ or 3H₂ gives, after recrystallization from an n-hexane solution, the chiral zirconium amides (2)Zr(NMe₂)₂ (9), (3)Zr(NMe₂)₂ (11), and titanium amide (3)Ti(NMe₂)₂ (10), respectively, in good yields. Reaction of Zr(NMe₂)₄ with 1 equiv of diphenylphosphoramide 4H₂ affords the chiral zirconium amide (4)Zr(NMe₂)₂ (12) in 85% yield. Under similar reaction conditions, treatment of Ti(NMe₂)₄ with 1 equiv. of sulphonylamide ligand, 5H₂ or 6H₂ gives, after recrystallization from a toluene solution, the chiral titanium amides (5)Ti(NMe₂)₂·0.5C₇H₈ (13·0.5C₇H₈) and (6)Ti(NMe₂)₂ (15), respectively, in good yields, while reaction of Zr(NMe₂)₄ with 1 equiv. of 5H₂ or 6H₂ gives the bis-ligated complexes, (5)₂Zr (14) and (6)₂Zr (16). Treatment of M(NMe₂)₄ with 2 equiv. of diphenylthiophosphoramide ligand 7H or N₃-ligand 8H gives, after recrystallization from a benzene solution, the bis-ligated chiral zirconium amides (7)₂Zr(NMe₂)₂ (17) and (8)₂Zr(NMe₂)₂ (19), and bis-ligated chiral titanium amide (8)₂Ti(NMe₂)₂ (18), respectively, in good yields. All new compounds have been characterized by various spectroscopic techniques, and elemental analyses. The solid-state structures of complexes 10, 12, 13, and 17-19 have further been confirmed by X-ray diffraction analyses. The zirconium amides are active catalysts for the asymmetric hydroamination/cyclization of aminoalkenes, affording cyclic amines in good to excellent yields with moderate ee values, while the titanium amides are not.     

Sc(OTf)3-catalyzed one-pot ene-Prins cyclization: a novel synthesis of octahydro-2H-chromen-4-ols

(R)-Citronellal undergoes initial ene reaction followed by Prins cyclization with aldehydes in the presence of 5 mol % of scandium triflate at ambient temperature to furnish octahydro-2H-chromen-4-ols in good yields and with high cis-selectivity. The use of scandium triflate makes this procedure simple, more convenient, and practical.     

De novo synthesis of teleocidin B analogs

Teleocidin B analogs have been synthesized in 24 steps and 1.9% overall yield. The key steps include aromatic Claisen rearrangement, intramolecular Heck reaction of a tetra-substituted alkene, and ruthenium (II) catalyzed indole cyclization. Teleocidin and the new analogs promote cell spreading on fibroblast cells that were treated with amino-Nogo, an inhibitor of cell spreading.     

Palladium-mediated reductive Mizoroki-Heck cyclization strategy for the regioselective formation of dibenzoazocinone framework

The synthesis of dibenzoazocine framework through palladium-mediated reductive Mizoroki-Heck cyclization has been described. The procedure is simple, straightforward, and regioselective.     

Intramolecular titanium-promoted deoxygenative cyclization to 9-substituted-1,2,3,4-tetrahydrofluorene skeleton

The Mukaiyama aldol reaction of 2-aryl-1-cyclohexene-1-carboxaldehydes with phenyl trimethylsilyl ketene acetal unexpectedly resulted in the formation of 9-substituted-1,2,3,4-tetrahydrofluorene derivatives via a novel intramolecular titanium-promoted deoxygenative cyclization. By successive treatment of the corresponding allyl alcohols with n-butyllithium and titanium tetrachloride, the cyclization products were obtained in good yields.     

A radical cyclization route to cyclic imines

A novel route to cyclic imines based on 5-exo radical cyclization is explored. The radical precursors are imines prepared from allylamine and readily available α-phenylselenenyl ketones.     

The silylalkyne-Prins cyclization: a novel synthesis of 4-iododihydropyrans

The silylated secondary homopropargylic alcohols undergo smooth coupling with aldehydes in the presence of molecular iodine under mild reaction conditions to produce 4-iododihydropyrans in good yields. This method is highly stereoselective, affording cis-dihydropyrans exclusively.     

Tuned C?H Functionalization to Construct Aza‐Podophyllotoxin/Aza‐Conidendrin Derivatives by Means of Domino Cyclization

An efficient domino cyclization method for the construction of aza‐podophyllotoxin/aza‐conidendrin derivatives has been established. Reactions of different dienes with aryl halides in the presence of a palladium catalytic system produced different kinds of podophyllotoxin derivatives through a highly regioselective C? H functionalization. Treatment of dienes with aryl halides that have electron‐withdrawing substituents on the phenyl ring created aza‐podophyllotoxin derivatives by means of the functionalization of the C? H bonds ortho to the C? halide bonds of the incoming aryl halides. The reaction of dienes with 1‐iodobenzene or aryl halides that incorporate electron‐donating groups produced aza‐conidendrin derivatives by means of the functionalization of both sp³ C? H and sp² C? H bonds. The regioselective C? H functionalization for the formation of different pseudo‐podophyllotoxin/‐conidendrin derivatives is proven by analyses of the ¹H NMR spectra of the products and selective X‐ray analyses of the structures of the products. Thus, the palladium‐catalyzed domino cyclization of 1,6‐dienes for the preparation of aza‐podophyllotoxin/aza‐conidendrin derivatives can be controlled by selectively controlling the C? H functionalization.     

Chromo‐Fluorogenic Detection of Nerve‐Agent Mimics Using Triggered Cyclization Reactions in Push–Pull Dyes

A family of azo and stilbene derivatives ( 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 ) are synthesized, and their chromo‐fluorogenic behavior in the presence of nerve‐agent simulants, diethylchlorophosphate (DCP), diisopropylfluorophosphate (DFP), and diethylcyanophosphate (DCNP) in acetonitrile and mixed solution of water/acetonitrile (3:1 v/v) buffered at pH 5.6 with MES, is investigated. The prepared compounds contain 2‐(2‐N,N‐dimethylaminophenyl)ethanol or 2‐[(2‐N,N‐dimethylamino)phenoxy]ethanol reactive groups, which are part of the conjugated π‐system of the dyes and are able to give acylation reactions with phosphonate substrates followed by a rapid intramolecular N‐alkylation. The nerve‐agent mimic‐triggered cyclization reaction transforms a dimethylamino group into a quaternary ammonium, inducing a change of the electronic properties of the delocalized systems that results in a hypsochromic shift of the absorption band of the dyes. Similar reactivity studies are also carried out with other “non‐toxic” organophosphorus compounds, but no changes in the UV/Vis spectra were observed. The emission behaviour of the reagents in acetonitrile and water–acetonitrile 3:1 v/v mixtures is also studied in the presence of nerve‐agent simulants and other organophosphorous derivatives. The reactivity between 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 and DCP, DCNP, or DFP in buffered water–acetonitrile 3:1 v/v solutions under pseudo first‐order kinetic conditions, using an excess of the corresponding simulant, are studied in order to determine the rate constants (k) and the half‐life times (t_1/2=ln2/k) for the reaction. The detection limits in water/acetonitrile 3:1 v/v are also determined for 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 and DCP, DCNP, and DFP. Finally, the chromogenic detection of nerve agent simulants both in solution and in gas phase are tested using silica gel containing adsorbed compounds 1 , 2 , 3 , 4 , or 5 with fine results.     

Diastero- and enantioselective intramolecular carbometalation reaction

The zinc-catalyzed addition of various alkynes to acylsilanes followed by a Zn-Brook rearrangement and either the Zn-ene-allene or Zn-yne-allene cyclization led to the enantio- and diastereoselective formation of carbocycles in a single-pot operation.