Stereoselective Preparation and Reactions of Configurationally Defined Dialkylzinc Compounds

Abstract

The reaction of cyclic and open-chain diastereomerically pure secondary organoboranes with diisopropylzinc allows the preparation of secondary dialkylzinc reagents with good to excellent retention of configuration as shown by deuterolysis and CuI- and Pd0-mediated reactions with electrophiles. The importance of a high boron-zinc exchange rate to obtain high diastereoselectivity has been shown. Improvement of the configurational stability and stereomeric purity of the zinc intermediates has been obtained by using mono-isopinocampheylborane ((-)-IpcBH2) providing optically active dialkylzinc compounds (up to 96% ee) with enhanced diastereoselectivities.

Asymmetric transition metal-catalyzed cross-coupling reactions for the construction of tertiary stereocenters

“…Notably, Knochel and co-workers have recently reported the diastereoselective arylation of substituted piperidines, an extension of the excellent cross-coupling methods developed by their laboratory for reactions with diastereomeric alkylzinc reagents. 54 …”

Nucleophilic Catalysis of the Iodine–Zinc Exchange Reaction: Preparation of Highly Functionalized Diaryl Zinc Compounds

“…After transfer of the first R group, with formation of RI and FG‐ArZnR, the nucleophilic catalyst Nu − Met + is regenerated, thus, in principle, making it possible to use this activator in catalytic amounts. We therefore treated methyl 4‐iodobenzoate ( 2 a ) with i Pr 2 Zn12 in Et 2 O/NMP (1:10) at 25 °C in the presence of various salts (Table 1). Mg(acac) 2 and MgCl 2 were found to be the most active magnesium additives (Table 1, entries 1–3 and 9), and Li(acac) to be by far the most active lithium additive (Table 1, entries 5–8).…”

Stereoselective Synthesis of anti‐1,4‐Diols by a BH3⋅THF‐Mediated Rearrangement of 1,2‐Disubstituted Cyclobutenes

“…Alkyllithium compounds, such as MeLi and EtLi, react in good yields providing cyclobutenes 3 e,f in 79 ± 84 % yield (entries 5 and 6, respectively). Organozinc derivatives, such as iPr 2 Zn, [8] react under copper catalysis after transmetallation with CuCN ¥ 2 LiCl to give the isopropylsubstituted cyclobutene 3 g in 74 % yield (entry 7). Even the reactive tertiary organolithium reagent tBuLi reacts well with 8 a to afford the corresponding cyclobutene 3 h in 73 % yield (entry 8).…”