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Reductive 1,2‐Allylboration of Indoles by Triallyl‐ and Triprenylborane − Synthesis of 2‐Allylated Indolines
Author(s) -
Bubnov Yury N.,
Zhun' Ilya V.,
Klimkina Elena V.,
Ignatenko Anatoly V.,
Starikova Zoya A.
Publication year - 2000
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/1099-0690(200010)2000:19<3323::aid-ejoc3323>3.0.co;2-k
Subject(s) - chemistry , allylic rearrangement , boranes , moiety , tautomer , yield (engineering) , double bond , indole test , stereochemistry , medicinal chemistry , organic chemistry , catalysis , boron , materials science , metallurgy
Indoles undergo reductive α‐allylation upon treatment with allylic boranes (triallyl‐ and triprenylborane) to give, after deboronation, the corresponding 2‐allylated indolines in 70−85% yield. 1,2‐Addition of the allylboron fragment to heterocycles occurs with full rearrangement of the allylic moiety. Reductive prenylboration of 3‐substituted indoles, as well as allylboration of 3‐isopropylindole, with All 3 B proceed stereoselectively to produce trans ‐2,3‐disubstituted indolines only, while similar reactions of triallylborane with 3‐R‐indoles, containing a primary group R, afford a mixture of trans (86−92%) and cis isomers (8−14%). From 1‐deuterioindole and triallylborane, a mixture of cis ‐ and trans ‐2‐allyl‐3‐deuterioindole in a ratio of 1:1 was obtained. Proposed mechanism of the general reaction involves intermediate formation of 3 H ‐indole tautomers followed by fast allylboration of the C=N bond. Structures of trans ‐indolines 3b and 3c were confirmed by X‐ray analysis.