Cu(I)‐Catalyzed Cross‐Coupling of Diazo Compounds with Terminal Alkynes: An Efficient Access to Allenes

Abstract

Cu(I)-catalyzed reaction of diazo compounds generates a Cu(I)-carbene intermediate that undergoes diverse transformations. In the past few years, the diazo compounds (or their precursor N-tosylhydrazones) have been established as cross-coupling partners under transition-metal catalysis, affording various organic compounds. Particularly the breakthrough has been made in allene synthesis by Cu(I)-catalyzed carbene coupling with terminal alkynes. Moreover, the Cu(I)-catalyzed coupling reaction of diazo compounds with terminal alkynes generates allene intermediate that undergoes tandem cyclization/coupling to afford cyclic compounds. This review article summarizes the most recent developments in allene synthesis based on the Cu(I)-carbene coupling reactions and the utilization of allene intermediates in tandem reactions.

Recent Advances in Catalytic Alkyne Transformation via Copper Carbene Intermediates

“…Transition-metal-catalyzed transformations of carbon-carbon triple bond have been presented as one of the most effective and prominent tools for the construction of functionalized molecules and fine chemicals [ 1 , 2 , 3 , 4 ]. Alkynes have low C sp –H p K a (~25), and the carbon-carbon triple bond could be selectively activated by π-acidic transition metals.…”

Synthesis of polyallenoates through copper-mediated cross-coupling of dialkynes and bis-α-diazoesters

“…10 In particular, copper-catalyzed carbene coupling has been proved as a reliable method for the synthesis of allenes. 11,12 Based on the copper-catalyzed carbene coupling strategy, the groups of Feng, Wang and Ley independently developed catalytic asymmetric synthesis of allenes. 13 In connection to our continuing interests in transition-metalcatalyzed carbene couplings and polymerizations, 14 we have conceived the application of the newly-developed carbene coupling reaction in the synthesis of allene-containing polymers.…”

Copper-Catalyzed Tandem Cross-Coupling and Alkynylogous Aldol Reaction: Access to Chiral Exocyclic α-Allenols

“…Copper-catalyzed cross-coupling reactions of terminal alkynes with diazo compounds represent one important protocol to synthesize polysubstituted allenes and allenoates. , A common accepted mechanism for the allene formation involves the formation of copper species I which undergoes migratory insertion to generate a propargyl copper species II (Scheme ). Subsequent protonation produces the final di- or trisubstituted allene (path a).…”

“…Also encouraged by Liu’s protocol, we envisioned that, by introducing a strong electrophile such as the aldehyde moiety into the alkyne molecule, the chiral exocyclic allenols bearing axially chiral allenes would be obtained through an effective catalytic system. As depicted in Scheme c, the reaction might start with the formation of copper species Int-2 via the preferential formation of copper acetylide Int-1 or copper-carbene Int-1′ , , which would undergo alkynyl migratory insertion to form propargyl copper species Int-3 . Then, the alkynylogous Aldol reaction would occur to yield the allenoate copper species Int-4 .…”