Reduction of alkynes with alkali metals in the presence of B 2 pin 2 results in diboration of alkynes. Distinct from conventional dissolving metal hydrogenations, two carbon−boron bonds and also two carbon−alkali metal bonds can be constructed in one operation to form 1,2diboryl-1,2-dimetalloalkanes. The 1,2-diboryl-1,2-dimetalloalkanes generated are readily convertible to a wide range of vicinal bis(boronate)s. In particular, oxidation of the 1,2dianionic species provides (E)-1,2-diborylalkenes, unique antiselective diboration of alkynes being thus executed.

A key step in amino sugar metabolism is the interconversion between fructose-6-phosphate (Fru6P) and glucosamine-6-phosphate (GlcN6P). This conversion is catalyzed in the catabolic and anabolic directions by GlcN6P deaminase and GlcN6P synthase, respectively, two enzymes that show no relationship with one another in terms of primary structure. In this study, we examined the catalytic properties and regulatory features of the glmD gene product (GlmD Tk ) present within a chitin degradation gene cluster in the hyperthermophilic archaeon Thermococcus kodakaraensis KOD1. Although the protein GlmD Tk was predicted as a probable sugar isomerase related to the C-terminal sugar isomerase domain of GlcN6P synthase, the recombinant GlmD Tk clearly exhibited GlcN6P deaminase activity, generating Fru6P and ammonia from GlcN6P. This enzyme also catalyzed the reverse reaction, the ammonia-dependent amination/isomerization of Fru6P to GlcN6P, whereas no GlcN6P synthase activity dependent on glutamine was observed. Kinetic analyses clarified the preference of this enzyme for the deaminase reaction rather than the reverse one, consistent with the catabolic function of GlmD Tk . In T. kodakaraensis cells, glmD Tk was polycistronically transcribed together with upstream genes encoding an ABC transporter and a downstream exo-␤-glucosaminidase gene (glmA Tk ) within the gene cluster, and their expression was induced by the chitin degradation intermediate, diacetylchitobiose. The results presented here indicate that GlmD Tk is actually a GlcN6P deaminase functioning in the entry of chitin-derived monosaccharides to glycolysis in this hyperthermophile. This enzyme is the first example of an archaeal GlcN6P deaminase and is a structurally novel type distinct from any previously known GlcN6P deaminase.Amino sugars, such as N-acetylglucosamine (GlcNAc), Nacetylgalactosamine (GalNAc), and N-acetylmuramic acid, are important building blocks for structural polysaccharides or sugar chains in several organisms. In the metabolism of these sugars, the conversion between fructose-6-phosphate (Fru6P) and glucosamine-6-phosphate (GlcN6P) is a key step in both anabolic and catabolic directions. The anabolic reaction is catalyzed by GlcN6P synthase (L-glutamine:D-fructose-6-phosphate amidotransferase), while catabolism is mediated by GlcN6P deaminase (Fig. 1A). GlcN6P synthase catalyzes the irreversible formation of GlcN6P and glutamate from Fru6P and glutamine and is classified in a glutamine-dependent amidotransferase family (18) comprised of an N-terminal glutamine amide transfer (GAT) domain joined to a C-terminal sugar isomerase domain (Fig. 1B). The former domain produces ammonia from glutamine, and the generated ammonia is utilized for amination of Fru6P accompanied by isomerization to GlcN6P in the latter domain. Unlike other glutamine-dependent amidotransferases displaying ammonia-dependent activity, GlcN6P synthase cannot utilize free ammonia as the nitrogen donor in place of glutamine (19).On the other hand, GlcN6P deaminase catalyzes the...

As a new transformation of organosulfur compounds, intramolecular desulfitative coupling of diaryl sulfones to the corresponding biaryls has been developed with the aid of nickel− NHC catalysts. This catalytic elimination of SO 2 was also applicable to alkenyl aryl sulfone to furnish the corresponding alkenyl arene.

Reductive 1,2-diboration of alkynes has been accomplished by means of sodium dispersion in the presence of trimethoxyborane as a reduction-resistant boron electrophile. Two boron moieties can be introduced onto alkynes with excellent syn selectivity to afford the corresponding (Z)-1,2-diborylalkenes. Bis(borate) species generated in situ can be involved in one-pot Suzuki-Miyaura arylation, formal arylboration of alkynes thus being executed.

An efficient and operationally simple method for the reduction of sulfoxides to sulfides has been developed using bis(catecholato)diboron (B 2 cat 2 ) as a reducing agent. The present method accommodates various functional groups which are generally prone to reduction: halides, alkynes, Organosulfur compounds have occupied important positions as bioactive entities, functional materials, and useful building blocks or reagents in organic synthesis. [1] Among organosulfur compounds, sulfoxides have attracted attention of synthetic chemists because of the unique reactivity as is seen in Swern oxidation [2] and Pummerer-type reactions. [3] Besides these classical reactions, sulfoxides are also utilized in asymmetric transformations as chiral auxiliaries. [4] Moreover, owing to the coordination ability to transition metals, sulfoxides promote catalytic C-H functionalizations as directing groups. [5] After these reactions, the sulfoxide moiety can be removed, which often accompanies the reduction of sulfoxides to sulfides and subsequent desulfurization. From that perspective, reduction of sulfoxides to sulfides is a simple yet important process in organic synthesis. [6] Although there are many reports on reduction of sulfoxides by means of metal hydrides [7] or low-valent transition metals, [8] these reactions intrinsically suffer from competing reduction of other functionalities such as carbonyls. Sulfur(II) compounds [9] and phosphines [10] are also known to promote the reduction of sulfoxides, but they often encounter purification problems. In the former case, separation of the resulting sulfide products from the remaining sulfur(II) reductants such as thiols and sulfides can be problematic. The latter faces the formation of phosphine oxides as by-products that are tedious to remove. Efficient methods achieving good functional group tolerance and facile purification of the products are of high demand.Recently we have been interested in the development of reductive transformations using diboron reagents. [11] During our investigation, we found that sulfoxides were reduced to the corresponding sulfides by means of diborons. Although there are two reports on the reduction of sulfoxides with bis(pinacolato)diboron (B 2 pin 2 ) as a deoxygenating reagent, [12] catalysts, long [a]