Zhengwang Chen

Silver-Catalyzed Difunctionalization of Terminal Alkynes: Highly Regio- and Stereoselective Synthesis of (Z)-β-Haloenol Acetates

A new silver-catalyzed highly regio- and stereoselective difunctionalization reaction of simple terminal alkynes was reported in which the (Z)-beta-haloenol acetate derivatives were formed efficiently. The resulting products were versatile intermediates in organic synthesis.

Palladium‐Catalyzed Bromoalkynylation of CC Double Bonds: Ring‐Structure‐Dependent Synthesis of 7‐Alkynyl Norbornanes and Cyclobutenyl Halides

The development of efficient and sustainable procedures for the synthesis of complex molecules is an important task in modern organic chemistry. The direct cleavage of an alkynyl– halogen bond followed by the reconnection of both the alkynyl and halogen ions with the two carbon atoms of an unsaturated carbon–carbon bond provides ready access to highly functionalized products from simple alkynes with excellent atom economy. We previously achieved highly regioand stereoselective bromoalkynylation of internal alkynes for the synthesis of conjugated cis-bromoalkenynes. Subsequent research on this subject revealed a further use of bromoalkynes in complex molecule synthesis. Norbornene derivatives are an appealing group of organic molecules that are convenient starting materials for the synthesis of polymers, solar-energy-storage materials, and bioactive products. In addition, their strained structure and high potential to coordinate to transition metals, as well as their possible industrial applications have attracted considerable research interest. Thus, we decided to react phenylethynyl bromide (2a) with norbornene (1a), expecting to obtain 2-bromo-3-(2-phenylethynyl)bicyclo[2.2.1]heptane (3aa ; Scheme 1). However, when using the previously optimized conditions, we did not detect the formation of 3aa, instead we obtained 2-bromo-7-(2-phenylethynyl)bicyclo[2.2.1]heptane (3a) in excellent yield, as confirmed by H NMR spectroscopy. This unexpected result attracted our interest, since, to the best of our knowledge, no example of a direct 7-alkynyl bromonorbornane formation has been reported. From previous reports, we realized that after the formation of the nonclassical “norbornonium” cation, the C-7 functionalization can be achieved through a nucleophile rearrangement (Scheme 2). Our success in synthesizing C-7-

Transition-Metal-Free Homocoupling of 1-Haloalkynes: A Facile Synthesis of Symmetrical 1,3-Diynes

Symmetrical 1,3-diyne compounds can be easily synthesized via a transition-metal-free homocoupling reaction of 1-haloalkynes without base and oxidant. The method shows excellent functional group compatibility and high yields.

Facile synthesis of benzofurans via copper-catalyzed aerobic oxidative cyclization of phenols and alkynes

Regioselective synthesis of polysubstituted benzofurans using a copper catalyst and molecular oxygen from phenols and alkynes in a one-pot procedure has been reported. The transformation consists of a sequential nucleophilic addition of phenols to alkynes and oxidative cyclization. A wide variety of phenols and alkynes can be used in the same manner.

Synthesis of 2,5-disubstituted 3-iodofurans via palladium-catalyzed coupling and iodocyclization of terminal alkynes.

2,5-Disubstituted 3-iodofurans are readily prepared under very mild reaction conditions by the palladium/copper-catalyzed cross-coupling of (Z)-β-bromoenol acetates and terminal alkynes, followed by iodocyclization. The useful intermediates conjugated enyne acetates are obtained in high yields in the transformation. Aryl- and alkyl-substituted alkynes undergo iodocyclization in good yields. The resulting iodine-containing furans can be readily elaborated to 2,3,5-trisubstituted furans.

PdCl2(HNMe2)2-catalyzed highly selective cross [2 + 2 + 2] cyclization of alkynoates and alkenes under molecular oxygen.

In the course of our study on palladium-catalyzed aerobic oxidation synthesis, we found that the PdCl(2)/O(2)/DMF system consistently experienced DMF hydrolysis to afford PdCl(2)(HNMe(2))(2), which is the real active catalyst for the aerobic oxidation. Although in situ DMF hydrolysis has been widely used in generating supramolecular assembly architectures, as far as we know, it is the first successful example to utilize PdCl(2)(HNMe(2))(2) in synthetic reactions. The highly selective cross [2 + 2+2] cyclization of alkynoates and different alkenes with electron-withdrawing groups could be smoothly catalyzed by PdCl(2)(HNMe(2))(2)/O(2)/DMF to afford the corresponding functionalized pentasubstituted benzenes in good to excellent yields (70-97%). The extension of alkyne surrogates for cross [2 + 2 + 2] cyclization from special alkenes with leaving groups to simple alkenes under molecular oxygen led to a paradigm shift in arene synthesis.

Transition-Metal-Free Semihydrogenation of Diarylalkynes: Highly Stereoselective Synthesis of trans-Alkenes Using Na2S·9H2O

A highly stereoselective and efficient transition-metal-free semihydrogenation of internal alkynes to E-alkenes using cheap and green water as hydrogen donor is described. The reactions are conducted under convenient conditions and provide products in good to excellent yields, with broad substrate scope, including a variety of diarylalkynes.

Cu(II)-Catalyzed Synthesis of Naphthalene-1,3-diamine Derivatives from Haloalkynes and Amines

An efficient procedure for the preparation of naphthalene-1,3-diamine derivatives by copper-catalyzed haloalkynes with amines has been reported. The reaction was supposed to proceed through a coupling reaction followed by the dimerization of ynamines.

Highly efficient synthesis of 2,5-disubstituted pyrazines from (Z)-β-haloenol acetates

A highly efficient synthesis of a wide range of 2,5-disubstituted pyrazines from (Z)-β-haloenol acetates is described. The reactions are conducted under convenient conditions and provide products with excellent regioselectivity in moderate to excellent yields with a broad substrate scope, including a variety of aromatic and aliphatic haloenol acetates.

Silver-catalyzed highly regioselective synthesis of α-carbonyl furans from enynones

Abstract A general and efficient method for the synthesis of a wide range of α-carbonyl furans is described here. The cyclization of enynone is catalyzed by AgBF4 in a fluorous biphasic system of perfluorodecalin and N,N-dimethylformamide. A variety of chain ketone and cyclic ketone substrates were used to investigate the scope of the reactions. GRAPHICAL ABSTRACT