Selective preparation of pyridine derivatives from two different alkynes and a nitrile was achieved by a novel procedure in which an alkyne and a nitrile couple first to give an azazirconacyclopentadiene followed by reaction with the second alkyne in the presence of 1 equiv of NiCl(2)(PPh(3))(2). This procedure gives only single products of pyridine derivatives from two different symmetrical alkynes and a nitrile. Our novel procedure can be used even with two similar alkyl-substituted alkynes such as 3-hexyne and 4-octyne. Two possible pyridine isomers from 3-hexyne, 4-octyne, and acetonitrile could be completely and independently prepared as single products by this method. The origin of the selectivity comes from the addition order of two different alkynes. This method was applied for the formation of pyridones and iminopyridines using isocyanate and carbodiimide derivatives instead of nitriles, respectively. Reaction of an alkyne with Cp(2)ZrEt(2) and an isocyanate or a carbodiimide gives an azazirconacycle. Treatment of the azazirconacycle with the second alkyne in the presence of 1 equiv of NiCl(2)(PPh(3))(2) gave a pyridone or an iminopyridine derivative. The use of two different unsymmetrical alkynes afforded the pyridine with five different substituents when the first alkyne has a trialkylsilyl group and the second alkyne has a phenyl group as functional groups. On the other hand, azazirconacyclopentadienes reacted with propargyl bromide in the presence of CuCl with excellent regioselectivity to give tetrasubstituted pyridine derivatives as single products. With the assistance of the trialkylsilyl groups, pyridines with all different substituents including H were also prepared.

Zirconacyclopentadienes, prepared from two alkynes or a diyne, reacted with the alkyl-, trimethylsilyl-, or alkoxy-substituted third alkyne as well as an alkyne with an electron-withdrawing group in the presence of a stoichiometric amount of NiBr 2 (PPh 3 ) 2 to give benzene derivatives in good yields. Heteroatom-containing diynes such as dipropargylbenzylamine and propargyl-homopropargylbenzylamine gave isoindoline and tetrahydroisoquinoline derivatives in good to high yields. This procedure was also used for the selective preparation of benzene derivatives from three different alkynes. The use of trimethylsilyl-substituted alkyne as the first, second or third alkyne afforded desilylated benzene derivatives. The reaction of zirconacyclopentadienes with allenes gave benzene derivatives as a mixture of two isomers.

A cationic 2,2¢-bipyridyl palladium(II)/CuI system was proven to be a reusable and highly efficient catalyst for the homocoupling of terminal alkynes at room temperature using water as a solvent in the presence of TBAB under aerobic conditions. For aromatic terminal alkynes, the reaction was performed either with or without I 2 as an oxidant; the addition of I 2 was required when aliphatic terminal alkynes were used as a substrate for the homocoupling reaction. In the presence of 0.0001-1 mol% palladium catalyst and 1 mol% CuI, a variety of terminal alkynes were homocoupled in good to excellent yields. The water-soluble catalytic system was separated from the organic products by extraction and the residual aqueous solution showed activity for reuse for several cycles without a significant decrease in activity.

Aerobic Conditions. -A geen method by using the environmentally friendly and cheap FeCl3·6H2O as catalyst for the synthesis of thioethers, e.g. (III), has potential for use in industrial applications. The catalytic system can be reused at least six times with only a slight derease in activity.

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A CoCl 2 ?6H 2 O/cationic 2,2'-bipyridyl system was proven to be an efficient and reusable catalyst for the coupling of aryl halides with thiols in water under aerobic conditions, leading to the formation of thioethers. Aryl iodides and bromides could couple with various thiols giving the corresponding thioethers using only a 3 mol% catalyst loading in the presence of 1 equiv KOH and 1.5 equiv Zn at 100 uC. For aryl chlorides, reaction at 140 uC and prolongation of the reaction time was performed. After reaction, the residual aqueous solution could be reused several times without any additional treatment and regeneration, making this cobalt-catalyzed S-arylation reaction greener.

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A water-soluble and air-stable Pd(NH3)2Cl2/cationic 2,2’-bipyridyl system was found to be a highly-efficient and reusable catalyst for the coupling of aryl iodides and alkenes in neat water using Bu3N as a base. The reaction was conducted at 140 °C in a sealed tube in air with a catalyst loading as low as 0.0001 mol % for the coupling of activated aryl iodides with butyl and ethyl acrylates, providing the corresponding products in good to excellent yields with very high turnover numbers. In the case of styrene, Mizoroki-Heck coupling products were obtained in good to high yields by using a greater catalyst loading (1 mol %) and TBAB as a phase-transfer agent. After extraction, the residual aqueous solution could be reused several times with only a slight decrease in its activity, making the Mizoroki-Heck reaction “greener”.