Zinc Reagents for Stereoselective Reactions

Stereoselective Rh2(S-IBAZ)4-Catalyzed Cyclopropanation of Alkenes, Alkynes, and Allenes: Asymmetric Synthesis of Diacceptor Cyclopropylphosphonates and Alkylidenecyclopropanes

“…Under these conditions, cyclopropane 6 was reproducibly obtained in 99% isolated yield, 97:3 dr and 99% ee, using only 1 mol % of Rh 2 ( S -IBAZ) 4 as catalyst. It is noteworthy that unlike most metal-catalyzed cyclopropanation reactions using diazo compounds, both our protocols do not require syringe-pump techniques or a large excess of one of the reagents. Indeed, α-cyano diazophosphonate 3 (1.5 equiv) is added within 5–10 min via syringe to the mixture containing the alkene (1 equiv) and the catalyst (1 mol %) in solution.…”

“…Despite the low propensity of allenes to undergo cyclopropanation reactions, we were delighted to observe the formation of E -alkylidenecyclopropane 34 in excellent yield and enantioselectivity (Table , entry 5, and Figure ) . While a vast array of catalytic methods exist for the enantioselective synthesis of cyclopropanes and cyclopropenes from diazo compounds, the corresponding alkylidenecyclopropanation reactions remain underexploited. In fact, this constitutes the first example of a catalytic enantioselective alkylidenecyclopropanation reaction using a diacceptor diazo compound.…”

“…In analogy to cyclopropylcarboxylates, the most efficient catalytic asymmetric methods for their formation involves the reaction of a monoacceptor diazophosphonate species with an alkene using chiral copper(I), ruthenium(II), , or rhodium(II) catalysts (Scheme a) . However, the enantioselective synthesis of the corresponding diacceptor cyclopropylphosphonates using such a strategy remains unexplored. , Because of the high potential of diacceptor cyclopropanes in asymmetric synthesis, either as precursors of ACC derivatives, or as substrates in stereospecific substitution , and formal cycloaddition reactions, we envisioned that access to their phosphonate-substituted analogues in enantioenriched form would be of considerable value.…”

Pd-Catalyzed Asymmetric Cyclopropanation Reaction of Acyclic Amides with Allyl and Polyenyl Carbonates. Experimental and Computational Studies for the Origin of Cyclopropane Formation

“…Cyclopropanes have widely been presented as the key subunit in many natural products and biologically active compounds, as well as used also as the important building block in organic synthesis . Many efficient protocols have been developed to prepare cyclopropane compounds. − However, the cyclopropanation reactions involving carbenes, carbenoids, and ylides intermediates are among the most important approaches. Pioneering work of Hegedus, the palladium-mediated cyclopropanation via attack of a nucleophile to the central carbon of allyl ligand of a π-allylpalladium chloride, revealed a new way to synthesize cyclopropanes (Scheme a) .…”