Optional Synthesis of 2- or 5-Substituted 3-Bromopyrroles via Bromine-Lithium Exchange of N-Benzenesulfonyl-2,4-dibromopyrrole
摘要:
The regioselective bromine-lithium exchange of N-benzenesulfonyl-2,4-dibromopyrrole (6) with n-BuLi followed by treatment with various electrophiles gave 5-substituted 3-bromopyrroles (5) in excellent yields. In contrast, the sequential treatment of 6 with n-BuLi and diisopropylamine followed by quenching with electrophiles produced regioisomeric 2-substituted 3-bromopyrroles (3) selectively. The latter reaction can be rationalized by the rapid equilibration of the C-5 lithio species (4) to the more stable C-2 lithio species (2) in the presence of diisopropylamine.
Directed Lithiation of <i>N</i>-Benzenesulfonyl-3-bromopyrrole. Electrophile-Controlled Regioselective Functionalization via Dynamic Equilibrium between C-2 and C-5 Lithio Species
Directed lithiation of N-benzenesulfonyl-3-bromopyrrole (1) with LDA in THF at -78 degrees C generated C-2 lithio species 3 selectively. Reactions of 3 with reactive electrophiles produced the corresponding 2-functionalized pyrroles 4. On the other hand, quenching with less reactive electrophiles generated the corresponding 5-substituted pyrroles 5. The latter unusual functionalization at C-5 could be rationalized by dynamic equilibrium between C-2 and C-5 lithio species,
Ethyl a-Amino-b,b-Diethoxypropionate, a Useful Synthon for the Preparation of 3,4-Fused Pyridine-6-carboxylates from Aromatic Aldehydes
作者:Robert H. Dodd、Sunil K. Singh、Mouloud Dekhane、Mireille Le Hyaric、Pierre Potier
DOI:10.3987/com-96-s30
日期:——
The second generation synthesis of a tumor promoter pendolmycin
作者:Kazuaki Okabe、Mitsutaka Natsume
DOI:10.1016/s0040-4020(01)88285-5
日期:1991.9
Totalsynthesis of a tumor promoter pendolmycin (1) was accomplished in the stereospecific manner using a d-serine derivative 7 and an l-valine derivative 16 as chiral sources. Methyl 2-(bromomethyl)benzoate was used for the critical step of the indole cyclization 25 → 26 and 28.
Optional Synthesis of 2- or 5-Substituted 3-Bromopyrroles via Bromine-Lithium Exchange of N-Benzenesulfonyl-2,4-dibromopyrrole
作者:Masatomo Iwao、Tsutomu Fukuda
DOI:10.3987/com-12-s(n)81
日期:——
The regioselective bromine-lithium exchange of N-benzenesulfonyl-2,4-dibromopyrrole (6) with n-BuLi followed by treatment with various electrophiles gave 5-substituted 3-bromopyrroles (5) in excellent yields. In contrast, the sequential treatment of 6 with n-BuLi and diisopropylamine followed by quenching with electrophiles produced regioisomeric 2-substituted 3-bromopyrroles (3) selectively. The latter reaction can be rationalized by the rapid equilibration of the C-5 lithio species (4) to the more stable C-2 lithio species (2) in the presence of diisopropylamine.