Figure 4: Formation of the exo-olefinic cyclopentenone product. | Nature Communications

Figure 4: Formation of the exo-olefinic cyclopentenone product.

From: Synthesis of tetrasubstituted 1-silyloxy-3-aminobutadienes and chemistry beyond Diels–Alder reactions

Figure 4

(a) Reactions were conducted with 0.05 mmol dienes in 1 ml solvent; isolated yield. (b) It is interesting that the closing ends of the iminium intermediates are both electron deficient. (c) Condition screening: MeSO3H (1.1 equiv.), DCM, 30%; CF3SO3H (1.1 equiv.), DCM, 35%; trifluoroacetic acid (TFA, 1.1 equiv.), DCM, 56%; TFA (1.1 equiv.), Et2O, 49%; TFA (1.1 equiv.), tetrahydrofuran (THF), 33%; TFA (0.5 equiv.), DCM, 30%; TFA (2.0 equiv.), DCM, 28%; TFA (5.0 equiv.), DCM, trace. (d) The products in the box were synthesized using 0.05 mmol dienes and 0.055 mmol TFA in 1 ml dichloromethane; isolated yield.

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