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45.28.1.1.7.2 Variation 2: Transition-Metal-Catalyzed Alkyne Cyclotrimerization

DOI: 10.1055/sos-SD-045-01348

Shinmyozu, T.; Shibahara, M.Science of Synthesis, (2010451279.

It is well-known that certain cyclophanes having short ansa chains exhibit planar chirality due to the restricted rotation of these chains. [6]Metacyclophane 45 (R1=CO2Et), obtained from deca-1,9-diyne and diethyl acetylenedicarboxylate in 50% yield by rhodium-catalyzed alkyne cyclotrimerization (at a concentration of 0.005M) using a bis(cyclooctadiene)rhodium(I) tetrafluoroborate/(R)-2,2-bis(diphenylphosphino)-5,5,6,6,7,7,8,8-octa­hydro-1,1-binaphthyl [(R)-H8-BINAP] system, is achiral due to flipping of the hexameth­ylene chain at room temperature. However, a similar cyclization, between 3-[2-(prop-2-yn­yloxy)ethoxy]prop-1-yne and dimethyl acetylenedicarboxylate (at a concentration of 0.01M), gives [6]metacyclophane 46 in appreciable enantiomeric excess (17% yield; 23% ee), although complete racemization is observed after 48hours at room temperature (Scheme 13).[‌32‌‌35‌]

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M M ee (%) Meeeee (%) Mee
M=M MM8 >88 88 (88) [‌88‌]
M=M (MM8)8 >88 88 (88) [‌88‌]
M=M (MM8)8 88 88 (88) [‌88‌]
M=M MM8MMM8 >88 88e (88) [‌88‌]
M=M (MM8)8 88 88 (88) [‌88‌]
MM8 MM8 88 88 (88) [‌88‌]
MM8 (MM8)8 88 88 (88) [‌88‌]
MM8 (MM8)8 88 88 (88) [‌88‌]
MM8 MM8MMM8 88 88e,e (88) [‌88‌]
MM8 (MM8)8 88 88e (88) [‌88‌]

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References


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