Reductive 1,2-allylboration of indoles by triallyl- and triprenylborane - Synthesis of 2-allylated indolines

Citation
Yn. Bubnov et al., Reductive 1,2-allylboration of indoles by triallyl- and triprenylborane - Synthesis of 2-allylated indolines, EUR J ORG C, (19), 2000, pp. 3323-3327
Citations number
27
Categorie Soggetti
Organic Chemistry/Polymer Science
Journal title
EUROPEAN JOURNAL OF ORGANIC CHEMISTRY
ISSN journal
1434193X → ACNP
Issue
19
Year of publication
2000
Pages
3323 - 3327
Database
ISI
SICI code
1434-193X(200009):19<3323:R1OIBT>2.0.ZU;2-U
Abstract
Indoles undergo reductive cc-allylation upon treatment with allylic boranes (triallyl- and triprenylborane) to give, after deboronation, the correspon ding 2-allylated indolines in 70-85 % yield. 1,2-Addition of the allylboron fragment to heterocycles occurs with full rearrangement of the allylic moi ety. Reductive prenylboration of 3-substituted indoles, as well as allylbor ation of 3-isopropylindole, with All(3)B proceed stereoselectively to produ ce trans-2,3-disubstituted indolines only while similar reactions of triall ylborane with 3-R-indoles, containing a primary group R, afford a mixture o f trans (86-92%) and cis isomers (8-14%). From 1-deuterioindole and trially lborane, 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 inte rmediate formation of 3H-indole tautomers followed by fast allylboration of the C=N bond. Structures of trans-indolines 3b and 3c were confirmed by X- ray analysis.