A general synthetic route to 6,6-substituted-6H-dibenzo[b,d]pyrans from dibenzofuran.
The reaction of dibenzofuran 1, lithium pieces (2.2 equiv), and TMEDA (2.2 equiv) in dry ether under reflux led to a solution of the corresponding C,O-dilithiated intermediate 2 which, upon treatment with different ketones or aldehydes (0.8 equiv) at -78 degrees C, afforded, after hydrolysis and dehydration, 6,6-substituted-6H-dibenzo[b,d]pyrans 3 in good yields. The reaction undergoes reductive ring opening and cyclization, and the intermediate diol 4e was isolated.
Wang
Bin
B
State Key Laboratory of Elemento-Organic Chemistry, College of Chemistry, Nankai University, Tianjin 300071, People's Republic of China.
Li
Minxiong
M
Xu
Shansheng
S
Song
Haibin
H
Wang
Baiquan
B
D001572:Benzofurans / Q000737:chemistry*; D008094:Lithium; D009942:Organometallic Compounds; D011714:Pyrans / Q000138:chemical synthesis*
D001572:Benzofurans; D009942:Organometallic Compounds; D011714:Pyrans; C450681:phenyllithium; C023614:dibenzofuran; D008094:Lithium