Alicia B. Chopa

Selective Synthetic Routes to Sterically Hindered Unsymmetrical Diaryl Ketones via Arylstannanes

Bulky arylstannanes and bulky aroyl chlorides are good reaction partners for the synthesis of two-, three-, and even four-ortho-substituted benzophenones, in good to excellent isolated yields (47-91%). Three simple and direct routes, with differential advantages, are proposed: (i) a catalyst-free protocol, in o-dichlorobenzene (ODCB) at 180 °C; (ii) a room temperature protocol, using AlCl(3) (0.5 equiv), in dichloromethane (DCM); and (iii) a solvent-free, indium-promoted procedure. A radical mechanism is proposed for the indium-mediated reactions.

Synthesis and some reactions of mixed (−)-menthyltin hydrides

Abstract The synthesis and physical properties of dineophyl(−)menthyltin ( 4 ) and methylneophyl (−)menthyltin ( 9 ) hydrides as well as that of their organotin precursors are described. Whereas the reduction of acetophenone with 4 afforded (−)-(S)-1-phenylethanol in 40% ee, the reduction of the same ketone with dimethyl(−)menthyltin hydride yielded the alcohol with only a 7% ee. Full 1 H, 13 C, and 119 Sn NMR data are given.

Antibacterial properties of water-soluble gold(I) N-heterocyclic carbene complexes

The antibacterial properties of water-soluble gold(I) complexes [1-methyl-3-(3-sulfonatopropyl)imidazol-2-ylidene]gold(I) chloride (C1), [1-mesityl-3-(3-sulfonatopropyl)imidazol-2-ylidene]gold(I) chloride (C2), [1-(2,6-diisopropylphenyl)-3-(3-sulfonatopropyl)imidazol-2-ylidene]gold(I) chloride (C3) and [1,3-bis(2,6-diisopropyl-4-sodiumsulfonatophenyl)imidazol-2-ylidene]gold(I) chloride (C4) and the respective ligands were assessed by agar diffusion and broth macrodilution methods against Gram-positives Staphylococcus aureus, Enterococcus faecalis and Micrococcus luteus and the Gram-negative bacteria Yersinia ruckeri, Pseudomonas aeruginosa and Escherichia coli. Viability after treatments was determined by direct plate count. The bactericidal activity displayed by C1 and C3 was comparable to that of AgNO3.

Efficient Catalyst-Free Bi- And Triaroylation of Aromatic Rings in a Single Step

The exceptional leaving group ability of the trimethylstannyl group in electrophilic aromatic substitutions makes possible the synthesis, in a single step, of bi- and triaroylarenes through the catalyst-free, regioselective reaction of bi- and tristannylarenes with different aroyl halides in o-dichlorobenzene as solvent. Specific di- and triketones are obtained in good to excellent yields (45-83%).

Organotin hydride additions to E- And Z-trisubstituted ethylenes synthesis of some new functionally substituted organotin compounds

Abstract The syntheses of some new functionally substituted organotin compounds are reported. The results indicate that the additions of tri-n-butyltin and tri-phenyltin hydrides to trisubstituted ethylenes (where one substituent is either a carbomethoxy or a nitrile group) proceed smoothly to give high yields of organotin adducts and that the reactions are stereoselective. Evidence concerning the reversibility of the free radical forming step is presented.

Indium-mediated regioselective synthesis of ketones from arylstannanes under solvent-free ultrasound irradiation.

The solvent-free indium-promoted reaction of alkanoyl chlorides with sterically and electronically diverse arylstannanes is a simple and direct method for the regioselective synthesis of primary, secondary and tertiary alkyl aryl ketones in good to excellent isolated yields (42-84%) under mild and neutral conditions. The protocol is also adequate for the synthesis of aryl vinyl ketones. Reaction times are drastically reduced (from 3-32h to 10-70min) under ultrasonic irradiation. Evidences for the involvement of a homolytic aromatic ipso-substitution mechanism, in which indium metal acts as radical initiator, are presented. It is possible the transference of two aryl groups from tin, thus improving effective mass yield, working with diarylstannanes as starting substrates.

Reactions of haloarenes, haloheteroarenes and dihalobenzenes with triphenylstannyl anions in DMSO and acetonitrile

Abstract We studied different haloarenes, haloheteroarenes and dihalobenzenes with Ph3Sn− ions in DMSO or acetonitrile (CH3CN) as solvents, in the dark or under irradiation to determine whether the halogen metal exchange (HME) reaction or the SRN1 process prevails. With p-chloroanisole the photostimulated reaction is sluggish in DMSO. There is an HME reaction with 2- and 3-chlorothiophene. Bromoarenes (p-bromoanisole, p-dibromobenzene and 1-bromonaphthalene) and p-iodoanisole react with Ph3Sn− ions faster by an HME mechanism than by the SRN1 process. In the photostimulated reaction of 1-chloronaphthalene, 2-chloro and 3-chloropyridines with Ph3Sn− ions in DMSO, the substitution products are obtained in 72, 82 and 93% yields, respectively. With p-dichlorobenzene the di-substitution product is obtained in 90% yield. All these reactions occur by the SRN1 mechanism. Yields improve when the reactions are carried out in DMSO rather than in CH3CN.

Chemo- and stereoselective reduction of (pivaloyloxy)methyl 6,6-dihalopenicillanates by trineophyltin hydride: Selective synthesis of 6β-halopenicillanates

Abstract A new Triorganotin hydride, Trineophyltin hydride was prepared and its chemo- and stereoselectivity towards reduction of Pom 6,6-homo- and hetero- dihalopenicillanates was examined. The trineophyltin hydride reveals higher stereoselectivity compared to that by tributyltin hydride at 25°C.

The reactions of diborane with aryl-organotin compounds

Abstract A number of tetraaryltin compounds, Ar 4 Sn (where Ar = phenyl, o - and p -tolyl, and p -chlorophenyl) and triphenyltin compounds, Ph 3 SnX (where X = Cl, H, OH, OCOCH 3 , and OCOCF 3 ) have been treated with diborane in tetrahydrofuran. Transmetallation occurs in which one or more aryl groups are transferred to boron. The organoboron intermediates give phenols upon oxidation and boronic and borinic acids upon hydrolysis. Pyridine complexes of organoboranes have also been isolated.

Ultrasound-assisted synthesis of unsymmetrical biaryls by Stille cross-coupling reactions

We describe herein an efficient method for the synthesis of unsymmetrically-substituted biphenyls using a sonochemical variation of the Stille coupling, whose results have also been compared with the conventional silent reaction. Ultrasound significantly enhances this useful organometallic transformation affording products in higher yields and in shorter reaction times than non-irradiated reactions. The scope has been explored with a selection of arylstannanes as precursors and, remarkably, no by-products resulting from homo-coupling could be detected.