Figure 4: Synthesis of the DHDG group.
From: A unified strategy for the synthesis of highly oxygenated diaryl ethers featured in ellagitannins
The first step is a subsequent oxa-Michael addition and elimination. Among all combinations with 7-Br and 7-I as the electrophiles and 8 and 9 as the nucleophiles, the combination of 7-Br and 8 was the optimal one. The second step is a chemoselective reduction of the orthoquinone monoketal in the presence of the other reducible functional groups. The ketal and adjacent alkene acted as an allyl ether to form a Pd-π-allyl complex, which conferred chemoselectivity. DMF=N,N-dimethylformamide; Et, ethyl.
