B(F)(F)F.CCOCC.[CH:10](=O)[CH2:11][CH2:12][CH3:13].C[Si](C)(C)[O:17][C:18]1[CH2:21][CH2:20][C:19]=1[O:22][Si](C)(C)C.C([O-])(O)=O.[Na+].C(O)(C(F)(F)F)=O>C(Cl)Cl>[CH2:11]([CH:10]1[C:19](=[O:22])[CH2:20][CH2:21][C:18]1=[O:17])[CH2:12][CH3:13]To a solution of BF3.OEt2 (1.30 g, 9.2 mmol) and butyraldehyde (0.40 g, 5.5 mmol) in DCM (5 ml) under N2 at −78° was added a solution of 1,2-bis trimethylsilyloxycyclobutene (1.4 g, 6.1 mmol) in DCM (3 ml) maintaining a temperature of less than −70°. After 2 h at −78° the solution was poured into saturated NaHCO3, extracted into EtOAc, washed (brine), dried (MgSO4) and the solution concentrated in vacuo to yield a clear liquid. To this liquid was added TFA (20 ml) and the solution heated at reflux for 24 h.
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