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. Author manuscript; available in PMC: 2021 Apr 7.
Published in final edited form as: Org Chem Front. 2020 Jan 2;7(7):913–918. doi: 10.1039/c9qo01336a

Table 1.

Reaction optimization for aldol elimination/ electrocyclization sequence.

graphic file with name nihms-1554065-t0009.jpg
Entry Base (equiv.) Solvent Temp. 2/3b
1 K2CO3 (3.0) Acetone reflux 1:2 (23)c
2 Et3N (3.0) DCM reflux N.R.
3 DBU (3.0) DCM rt 95:5
4 DBU (3.0) DMSO rt 90:10
5 DBU (3.0) DMSO rt → 80 °C 0:100 (82)c
6 DBU (2.0) DMSO rt → 80 °C 0:100 (64)c
7 DBU (1.0) DMSO rt → 80 °C 0:100 (45)c
8 DBU (0.1) DMSO rt → 80 °C trace
a

All optimization reactions were performed by adding base at room temperature to a solution of 1 in DMSO (0.15 M). The reaction vessel was sealed and heated at the indicated temperature for 16 hours.

b

The percent ratio of 2 and 3 was determined by crude 1H NMR integration.

c

Isolated yield of 3 obtained after column chromatography.

N.R. = No reaction