Metal-free POCl3 promoted stereoselective hydrochlorination of ethynylated azaheterocycles.

An efficient hydrochlorination of ethynylated azaheterocycles was achieved using POCl3 as a chlorinating agent under metal-free reaction conditions. Mechanistic studies show that the reaction proceeded via nucleophilic attack of POCl3 on the nitrogen of the quinoline ring in a stereoselective manner. The resulting products were versatile intermediates in organic synthesis and were used in the cross-coupling reaction and metal-free synthesis of heterocycles. The developed protocol features inexpensive and easily synthesizable starting materials, easy operation, and high efficiency with a high yield of products.

Pd-Catalyzed One-Pot Stepwise Synthesis of Benzo[b][1,6]naphthyridines from 2-Chloroquinoline-3-carbonitriles Using Sulfur and Amines As Nucleophiles.

A palladium-catalyzed one-pot stepwise coupling-annulation reaction of 2-chloroqunoline-3-carbonitriles enabled the direct synthesis of sulfur-substituted benzo[b][1,6]naphthyridines via multiple bond formation. The reaction provided an unusual mode for cyclization as sodium sulfide, a soft nucleophile, preferred to attack on the carbon of the nitrile group rather than on the C-C triple bond. The developed chemistry was extended with the secondary amines as nucleophiles to afford nitrogen-substituted benzo[b][1,6]naphythyridines while primary amines afforded hydroamination products . The hydromination products were transformed to benzo[b][1,6]naphthyridones via a base-mediated cyclization reaction. The  developed protocol features inexpensive and easily synthesizable starting materials, easy operations, and a high efficiency and tolerance to a broad range of substrates.

Na2S-mediated synthesis of terminal alkynes from gem-dibromoalkenes.

The Na2S-mediated facile synthesis of terminal alkynes from gem-dibromoalkenes, at 20/40 °C under open flask conditions has been developed. Various precursors derived from heteroaromatic/aromatic/aliphatic aldehydes were found compatible. The reaction is proposed to proceed through the Fritsch-Buttenberg-Wiechell (FBW) rearrangement involving the corresponding vinyl carbene. Using mild reaction conditions with inexpensive Na2S·9H2O under air atmosphere has significant advantages over earlier routes.

Metal free TBHP-promoted intramolecular carbonylation of arenes via radical cross-dehydrogenative coupling: synthesis of indenoquinolinones, 4-azafluorenones and fluorenones.

A metal-free, TBHP-promoted economical route is developed via the sp(2) C-H bond functionalization strategy for the synthesis of indenoquinolinones, 4-azafluorenones and fluorenones. Reactions provided excellent yield of the products under mild conditions. We have successfully synthesized 11H-indeno[1,2-b]quinolin-11-one, an antibacterial agent, in excellent yields.

Copper-free palladium-catalyzed Sonogashira coupling-annulation: efficient one-pot synthesis of functionalized pyrano[4,3-b]quinolines from 2-chloro-3-formylquinolines.

A convenient, one-pot, copper-free, Pd-catalyzed methodology has been described for the synthesis of 1,3-disubstituted pyrano[4,3-b]quinolines from 2-chloro-3-formylquinolines. Formation of annulated products 3 is attributed to the presence of Pd(OAc)2 and PPh3. Further, PPh3 in the reaction mixture promotes the cyclization by reducing the reaction time and increasing the yield of cyclized product.