Yehoshua Ben-David

Reductive dechlorination of aryl chlorides catalyzed by palladium complexes containing basic, chelating phosphines

Abstract Aryl chlorides undergo efficient, homogeneously catalyzed reductive dechlorination to the corresponding arenes using Pd(dippp) 2 as catalyst [dippp=1,3-bis(diisopropylphosphino) propane], which may be generated in situ from Pd(OAc) 2 and two equivalents of dippp. Two reducing systems are described: (a) sodium hydroxide in methanol; (b) sodium formate in alcohol or DMF. Base-sensitive functional groups (CHO, CN) do not survive the conditions of system (a), but remain unaffected during dechlorination with sodium formate. Various functional groups are tolerated, and high yields are obtained. The reaction rate is retarded by electron-donating substituents, indicating a rate-determining oxidative addition step. Reaction of the model complex (dippp)Pd(Ph)Cl with sodium formate in the presence of dippp leads to the formation of Pd(dippp) 2 and benzene. Dippp homologues are also effective ligands in the catalytic reaction, the reactivity order being dippp > dippb > dippe. Iso-Pr 3 P is only marginally effective. A mechanistic interpretation of these observations is given.

A new total synthesis of (±) steganone

Abstract A new total synthesis of (±) steganone was completed by a route involving the cyclization of a 2,2′-bis(bromoacyl)biaryl derivative.

Formation of P,C-chelated palladium complexes by phosphine-assisted oxidative addition of an aliphatic CCl bond

Abstract Reactions of the (chloralkyl) phosphine 1-chloro-3-(diisopropylphosphino)propane (3) with chelated Pd(0) complexes have been given, leading to P,C-chelated complexes. Reaction of a methyl-π-allypalladium chloride dimer with 1,3-(diisopropylphosphino)propane and a base gives the binuclear complex 2a. Pd(dippe)2 (dippe = 1,2-bis(diisopropylphosphino)ethane) reacts with 3 to yield the mononuclear bis-chelated complex 6. As expected, the intramolecular coordinatively oxidative addition of the aliphatic CCl bond in 3 to the metal center is much faster than that of the intermolecular reaction of n-butyl chloride. The X-ray structure of 2a was determined.

Formylation of aryl chlorides catalysed by a palladium complex

The complex (dippp)2Pd [dippp = 1,3-bis(di-isopropylphosphino)propane] is an efficient, unique catalyst for direct formylation of aryl chlorides to aldehydes with CO and sodium formate.

A novel route to linear polycyclic compounds. Diastereoselective aldol-type reactions of α-sulfonyl carbanions

Abstract Aromatic derivatives, bifunctionalized at vicinal benzylic positions with Br and SO 2 PH groups undergo one-pot annulations with unactivated cycloalkanones. The ring closure occurs by a diastereoselective aldol-type reaction of α-sulfonyl carbanions.

Reactions of sulfur-containing carbanions with ethyl 4-bromocrotonate. A facile synthesis of cyclopropanecarboxylates

Abstract Ethyl 4-bromocrotonate reacts as a Michael acceptor with carbanions derived from phenylsulfones and β-ester sulfides; the conjugated addition is followed by the displacement of Br − affording various cyclopropanecarboxylates.

Total synthesis of the lignan (±)-schizandrin

A total synthesis of (±)-schizandrin (1), a bisbenzocyclo-octadiene lignan of biological interest, has been completed starting from the diketone (2).

‘Caging’ of and catalysis by a complex inside a polymer matrix

Utilizing solvent dependent swelling, it is possible to physically trap molecules inside a polystyrene matrix: catalysis by a ‘caged’ rhodium complex is demonstrated.

New annulation methods of aromatic rings. New syntheses of naphthalene, anthracene and phenanthrene structures.

Abstract Condensation of 2-(phenylsulfonyl)methyl benzyl bromide and its derivatives with nalonates, 1,3-ketoesters and lactones resulted in the regioselective formation of naphthalene derivatives and of other polycyclic systems.