N-(Triisopropylsilyl)pyrrole. A progenitor "par excellence" of 3-substituted pyrroles
作者:Brian L. Bray、Peter H. Mathies、Reto Naef、Dennis R. Solas、Thomas T. Tidwell、Dean R. Artis、Joseph M. Muchowski
DOI:10.1021/jo00313a019
日期:1990.12
A very effective strategy has been devised for the synthesis of 3-substituted pyrroles based on the use of the triisopropylsilyl (TIPS) moiety as a sterically demanding nitrogen substituent to obstruct the attack of electrophilic reagents at the alpha-positions. 1-(Triisopropylsilyl)pyrrole (1) undergoes highly preferential kinetic electrophilic substitution at the beta-position with a variety of electrophiles (Br+, I+, NO2+, RCO+, etc.) and fluoride ion induced desilylation of the products provides the corresponding 3-substituted pyrroles in good overall yields. Competitive trifluoroacetylation experiments demonstrate that substitution of TIPS-pyrrole at the alpha-positions is decelerated by a factor of > 10(4), vs pyrrole at the same sites, without affecting reactivity at the beta-positions. 1-(Triisopropylsilyl)-3-bromopyrrole (2) is readily converted into the 3-lithio compound 44 by bromine-lithium interchange with alkyllithium reagents. This previously unavailable, formal equivalent of 3-lithiopyrrole is itself an excellent source of a wide range of beta-substituted pyrroles, many of which would not be directly preparable from 1. TIPS-pyrrole can be 3,4-dihalogenated and these compounds undergo sequential halogen-metal interchange trapping reactions. This process is exemplified by an efficient, three-step synthesis of the antibiotic verrucarin E (63) from the dibromo compound 5.
BRAY, BRIAN L.;MATHIES, PETER H.;NAEF, RETO;SOLAS, DENNIS R.;TIDWELL, THO+, J. ORG. CHEM., 55,(1990) N6, C. 6317-6328
作者:BRAY, BRIAN L.、MATHIES, PETER H.、NAEF, RETO、SOLAS, DENNIS R.、TIDWELL, THO+
DOI:——
日期:——
3-Lithiopyrroles by Halogen-Metal Interchange of 3-Bromo-1-(triissopropylsilyl)pyrroles. Synthesis of Verucarin E and Other 3-Substituted Pyrroles. Preliminary Communication
作者:Joseph M. Muchowski、Reto Naef
DOI:10.1002/hlca.19840670430
日期:1984.6.20
3-Lithio-1-(trimethylsilyl)pyrrole (7, Schem 2), obtained by halogen-metal interchange from the 3-bromo compound 2, reacted with various electrophilic reagents to provide products, which on fluoride ion desilylation, gave 3-substituted pyrroles in good overall yields. One such pyrrole 13 (Schem 3), was converted into 2-formyl-3-octadeclpyrrole (14), reputed to be a metabolite of the marine sponge Oscarella