Diethylzinc

Abstract

(A) 1,2-Addition: Seebach and co-workers reported the 1,2-addition of diethylzinc to aliphatic and aromatic aldehydes in the presence of Ti(Oi-Pr)4 and TADDOL derivatives as ligands, which led to enantiopure alcohols in good yields.4 Walsh and co-workers described also the synthesis of tertiary alcohols by the asymmetric addition of ZnEt2 to ketones catalyzed by a titanium catalyst with a chiral diamine ligand. (B) 1,4-Addition to Cyclic Enones: Alexakis and co-workers reported an asymmetric copper-catalyzed 1,4-addition of diethylzinc to cyclic enones using a phosphoramidite ligand, followed by C-enolate trapping resulting in the synthesis of α,β-disubstituted ketones with a high degree of stereoselectivity (C) 1,4-Addition to Reactive Acceptors: Carreira and co-workers developed the copper-catalyzed highly stereoselective conjugate addition of diethylzinc to Meldrum's acid derived acceptors with phosphoramidite ligands. (D) Addition to ?-Chloro Aldimines: Walsh and co-workers described a highly diastereoselective synthesis of ?-chloro amine via a nucleophilic addition to α-chiral imine derivatives that proceeds through an unusual chelation transition state instead of a Cornforth- Evans model. (E) Addition to N-Acylpyridinium Salts: Feringa and Minnaard developed a catalytic enantioselective addition of diethylzinc to N-acylpyridinium salts with good yields and excellent enantioselectivities. This method was applied to the synthesis of natural alkaloids. (F) Marshall Homopropargylation: Taking advantage of zinc(II)'s ability to perform transmetalation, allenyl zinc compounds were synthesized from diethylzinc. Then, addition to an aldehyde gave the desired anti homopropargylic alcohol adducts with high de. Marshall and co-workers synthesized various enantioenriched homopropargylic alcohols and applied this method to the synthesis of superstolide A.10 (G) Alkyl Radical Addition: Stereoselective synthesis of diethyl fumarate derivatives was accomplished under mild conditions via a direct anti carbozincation of diethyl acetylenedicarboxylate through diethylzinc-mediated alkyl radical addition. (H) Phenyl Transfer to Aldehydes: Bolm and co-workers have shown that in the synthesis of diarylmethanol compounds the use of diethylzinc can improve the enantioselectivity of the reaction.12 (I) Simmons-Smith Reaction: ZnEt2 was also used in asymmetric Simmons-Smith reactions.13 This reaction was employed in many syntheses of natural products: for instance in 2008, Willis and coworkers described the synthesis of (?)-clavosolide D: 14 treatment of the allylic alcohol with Et 2Zn and CH2ICl led to the formation of a cyclopropane with excellent yield and diastereoselectivity. (J) Enantioselective Allylic Substitution: In 2009, the group of Hoveyda reported that chiral N-heterocyclic carbene complexes are efficient catalysts in the copper-free enantioselective allylic alkylation using diethylzinc and allylic phosphates. This reaction led to enantioenriched allylic moieties with quarternary centers.15. © Georg Thieme Verlag Stuttgart. New York.