Noncryogenic Conditions Research Articles

Selective metal-halogen exchange of 4,4′-dibromobiphenyl mediated by lithium tributylmagnesiate

A selective metal–halogen exchange/electrophilic quench protocol on 4,4′-dibromobiphenyl 4 that proceeds under non-cryogenic conditions is reported. This method provides an economic alternative to traditional transition-metal catalyzed cross-coupling chemistry to prepare various biaryls 7a– g. This novel route to functionalized biaryls was used as the basis for the kg-scale preparation of a biphenyl ketone 1, a key intermediate in the synthesis of a potent cathepsin K inhibitor.

Bromine–magnesium exchange of 5-bromo-2-picoline via an organomagnesium complex nBu2iPrMgLi: a new preparation methodology of functionalized picolines under noncryogenic conditions

The organomagnesium complex nBu2iPrMgLi, readily prepared from nBuLi and iPrMgCl (2:1), is quite efficient for the bromine–magnesium exchange of 5-bromo-2-picoline under noncryogenic conditions (at −10°C). The resulting picolylmagnesium complex reacts with various electrophiles to afford functionalized picolines.

A novel and facile one-pot synthesis of pyridylselenium compounds through selective bromine–magnesium exchange with isopropylmagnesium halide

One-pot synthesis of various unsymmetrical 2-bromo-5-pyridylselenium compounds has been carried out under non-cryogenic conditions by selective single bromine–magnesium exchange of 2,5-dibromopyridine using isopropylmagnesium chloride. This exchange gives 2-bromo-5-pyridylmagnesium chloride, which upon the insertion of elemental selenium followed by the treatment with alkyl halide gives the title compounds in good yield. This exchange has also been extended towards bromine–magnesium exchange of 2-bromopyridine for the improved synthesis of 2-pyridylselenium compounds. The molecular structure of 2-bromo-5-selenopyridyltribromomethane has been examined by single crystal X-ray diffraction. This compound crystallizes in the monoclinic space group P21/n. From the molecular structure it was found that intermolecular BrBr, NSe and SeBr interactions control its crystal packing. Copyright © 2005 John Wiley & Sons, Ltd.

Regioselective synthesis of symmetrical pyridyl selenium compounds by bromine–magnesium exchange of bromopyridines using isopropyl magnesium chloride: X‐ray crystal structure of 2,2′,5,5′‐tetrabromo‐3,3′‐dipyridyldiselenide

Abstract2,2′‐Dipyridyl‐3,3′‐dipyridyl,5,5′‐dipyridyl‐diselenides have been synthesized by a convenient method employing non‐cryogenic conditions. Various bromopyridines (2‐Bromopyridine, 2,5‐dibromopyridines and 2,3,5‐Tribromopyridines) undergo selective monobromine–magnesium exchange to yield the corresponding pyridyl magnesium chlorides at room temperature upon treatment with iPrMgCl. The resulting pyridyl magnesium chloride is quenched with elemental selenium, which upon further oxidation affords the above diselenides in good yields. The compounds prepared using this methodology have been characterized by elemental analysis, IR, NMR (1H, 13C, 77Se) and mass spectral analysis. The molecular structure of 2,2′,5,5′‐Tetrabromo‐3,3′‐dipyridyldiselenide has been established by single‐crystal X‐ray diffraction analysis. It exists as a dimeric form due to the non‐bonding interactions between the selenium of one pyridine moiety and the hydrogen of the other. Copyright © 2004 John Wiley & Sons, Ltd.

A novel and convenient synthesis towards 2-pyridylselenium compounds: X-ray crystal structure of 4,4′-dimethyl-2,2′-dipyridyl diselenide and tris(2-pyridylseleno)methane

Various 2,2′-dipyridyl diselenides were prepared by a simple and convenient method employing non-cryogenic conditions. The diselenide anion, Se 2 2− formed by reducing elemental selenium with 100% hydrazine hydrate in sodium hydroxide reacts in situ with 2-bromopyridines to afford the title compounds in good to excellent yields. Hydrazine hydrate readily cleaves the selenium-selenium bond in these diselenides to generate 2-pyridylselenolate anion, which reacts with halomethanes to afford 2-pyridylseleno methanes. X-ray crystal structure of 4,4′-dimethyl-2,2′-dipyridyl diselenide ( 4) and tris(2-pyridylseleno)methane ( 10) is described.

Tributylmagnesium ate complex-mediated novel bromine–magnesium exchange reaction for selective monosubstitution of dibromoarenes

Lithium tributylmagnesate complex ( n-Bu 3MgLi), readily prepared from n-BuLi and n-BuMgCl (2:1), is a novel metallation agent. It is quite efficient for the selective mono-bromine–magnesium exchange of 2,6-dibromopyridine ( 1 ) under non-cryogenic conditions (at −10°C) to give a stable magnesate intermediate. Subsequent treatment with DMF gave 6-bromo-2-formylpyridine ( 3 ) in excellent yield. This method is also applicable for selective monosubstitution of several other kinds of dibromoarenes.