Phosphazene Base tBu-P4 Catalyzed Methoxy–Alkoxy Exchange Reaction on (Hetero)Arenes

The organic superbase tBu-P4 catalyzes methoxy-alkoxy exchange reactions on (hetero)arenes with alcohols. The catalytic reaction proceeded efficiently with electron-deficient methoxy(hetero)arenes as well as with a variety of alcohols, including 3-amino-1-propanol, β-citronellol, menthol, and cholesterol. An intramolecular version of this reaction furnished six- and seven-membered ring compounds.     

Synthesis and Spectroscopic Studies of Arylethynylsilanes

A variety of arylethynylsilanes (Ar‐C?C? C₆H₄? C?C)_nSiMe_4?n were prepared successfully by reaction of the corresponding chlorosilanes Me_4?nSiCl_n with Ar? C?C? C₆H₄? C?CM (M=Li, MgBr), which was prepared by treatment of ethynyl(diarylethyne)s Ar? C?C? C₆H₄? C?CH with BuLi or MeMgBr. The ethynyl(diarylethyne)s were readily prepared in good yields by the double‐elimination method: addition of lithium hexamethyldisilazide to a mixture of ArCH₂SO₂Ph, TMS? C?C? C₆H₄? CHO, and ClP(O)(OEt)₂, followed by desilylation. In the tetrakis(arylethynyl)silanes (Ar? C?C? C₆H₄? C?C)₄Si thus prepared, through‐space conjugation of four triple bonds on the silicon atom emerges as a result of participation of the silicon orbitals in the acetylenic π orbitals. This participation enhances the emissive quantum yields of arylethynylsilanes with an increase in the number of arylethynyl moieties on silicon: quantum yields of emission (Φ_F) of 0.72 for (MeOC₆H₄? C?C? C₆H₄? C?C)₄Si, 0.53 for (MeOC₆H₄? C?C? C₆H₄? C?C)₂SiMe₂, and 0.47 for MeO‐C₆H₄? C?C? C₆H₄? C?CSiMe₃ were obtained. Although this enhancement effect was also observed in the phenylethynylarylsilane (MeOC₆H₄? C?C? C₆H₄)₂SiMe₂, the bis(arylethynyl)disilane (MeOC₆H₄? C?C? C₆H₄? C?C‐SiMe₂)₂ exhibited non‐enhanced emission.     

Direct Carboxylation of Electron-Rich Heteroarenes Promoted by LiO-tBu with CsF and [18]Crown-6

We herein demonstrate that the combination of LiO-tBu, CsF, and [18]crown-6 efficiently promotes the direct C−H carboxylation of electron-rich heteroarenes (benzothiophene, thiophene, benzofuran, and furan derivatives). A variety of functional groups, including methyl, methoxy, halo, cyano, amide, and keto moieties, are compatible with this system. The reaction proceeds via the formation of a tert-butyl carbonate species.     

Octapalladium Strings Trap C60 and C70 Fullerenes Affording Metal-Chain-Wired Bucky Balls

Reactions of Pd₈ strings supported by meso-Ph₂PCH₂P(Ph)CH₂P(Ph)CH₂PPh₂ (meso-dpmppm) ligands, [Pd₈(meso-dpmppm)₄(L)₂]⁴⁺ (L=CH₃CN ( 1 ), XylNC ( 2 )) with C₆₀ resulted in the exclusive formation of unprecedented metal-chain-wired C₆₀ bucky balls, [{Pd₄(meso-dpmppm)₂(L)}₂(C₆₀)]⁴⁺ (L=CH₃CN ( 11 ), XylNC ( 12 )), in which a C₆₀ fullerene is trapped in the central Pd–Pd junction, as unambiguously established by spectroscopic, X-ray crystallographic, and theoretical techniques. The similar reaction of Pd₈ strings supported by rac-dpmppm, [Pd₈(rac-dpmppm)₄(CH₃CN)₂]⁴⁺ ( 3 ) also afforded a racemic mixture of [{Pd₄((R*,R*)-dpmppm)₂(CH₃CN)}₂(C₆₀)]⁴⁺ ( 13 ) without scrambling the Pd₄ fragments with (R,R)- and (S,S)-dpmppm ligands. Consequently, those of enantiopure chiral Pd₈ strings, [Pd₈((R*,R*)-dpmppm)₄(CH₃CN)₂]⁴⁺, certainly afforded chiral bucky balls of [{Pd₄((R*,R*)-dpmppm)₂(CH₃CN)}₂(C₆₀)]⁴⁺ ( 13 _RR and 13 _SS ), that exhibit mirror-image circular dichroism spectra. The reactions of 1 and 2 were also applied for trapping a C₇₀ fullerene to give 2 : 1 adducts of [{Pd₄(meso-dpmppm)₂(L)}₂(C₇₀)]⁴⁺ (L=CH₃CN ( 21 ), XylNC ( 22 )). These results provide useful information for creating a platform to develop dimensionally and chirality controlled metal–carbon nanocomposite materials.     

Glycosylated tris-bipyridine ferrous complexes as molecular mimics of densely packed glycoclusters on cell surfaces: spatial carbohydrate packing of glycoclusters changes on additions of salts

Tris-bipyridine ferrous complexes having β-lactosides, β-maltosides or α-mannosides with serinol spacers were prepared as molecular mimics of densely packed carbohydrate clusters on cell surfaces. Conformational analysis on these glycosylated complexes were conducted by UV–vis and circular dichroism spectroscopy measurements, which disclosed that the chloride, nitrate and sulfate salts induced the conformational changes of the glycosylated complexes in the anion- and carbohydrate-dependent manners.     

Photoinduced addition and addition–elimination reactions of perfluoroalkyl iodides to electron-deficient olefins

Photoinduced radical perfluoroalkylation of various simple electron-deficient olefins was achieved in the presence of an aqueous Na₂S₂O₃ solution. The reactions proceeded smoothly to give addition or addition–elimination products. The ability of the products to be used as radical precursors or Michael acceptors was also demonstrated.     

(E)‐,(Z)‐Parallel Preparative Methods for Stereodefined β,β‐Diaryl‐ and α,β‐Diaryl‐α,β‐unsaturated Esters: Application to the Stereocomplementary Concise Synthesis of Zimelidine

Parallel and practical methods for the preparation of both (E)‐ and (Z)‐β‐aryl¹‐β‐aryl²‐α,β‐unsaturated esters 1 and (E)‐ and (Z)‐α‐aryl¹‐β‐aryl²‐α,β‐unsaturated esters 2 are described. These methods involve accessible, robust, stereocomplementary N‐methylimidazole (NMI)‐mediated enol tosylations (14 examples, 70–99 % yield), as well as stereoretentive Suzuki–Miyaura cross‐couplings (36 examples, 64–99 % yield). The highlighted feature of the present protocol is the use of parallel and stereocomplementary approaches to obtain highly (E)‐ and (Z)‐pure products 1 and 2 by utilizing sequential enol tosylations and cross‐coupling reactions. An expeditious and parallel synthesis of (E)‐ and (Z)‐zimelidine ( 3 ), which is a highly representative selective serotonin reuptake inhibitor (SSRI), was performed by utilizing the present methods.     

Synthesis of Glycocinnasperimicin D

The first total synthesis of amino sugar antibiotic glycocinnasperimicin D ( 1 ) has been achieved by a convergent, three‐component coupling strategy. The key steps involve the Heck–Mizoroki reaction by using the iodophenyl glycoside 50 and acryl amide 32 to furnish the right core structure of 1 , and the construction of the urea glycoside employing the reaction of glycosyl isocyanate 8 with amino sugar 9 . Glycosyl isocyanate 8 was prepared by the oxidation of isonitrile 10 , which displayed excellent reactivity in the coupling event. Synthetic roadblocks, encountered during this synthetic effort, have led to the development of the α‐selective, Lewis acid catalyzed phenyl glycosylation process with 2‐amino‐hexopyranose and a procedure for acetonide deprotection without affecting the silyl ethers.     

Catalytic asymmetric desymmetrization of meso-diamide derivatives through enantioselective N-allylation with a chiral pi-allyl Pd catalyst: improvement and reversal of the enantioselectivity

In the presence of the Trost ligands-Pd catalysts, N-monoallylation of bis(2,4,6-triisopropylbenzne)sulfonylamides derived from meso-1,2-diamines proceeds with good to excellent enantioselectivity (85-96% ee) to give asymmetric desymmetrization products. Under the same conditions, in the reaction with meso-bistolunesulfonylamide derivatives, reversal of the enantioselectivity is observed.