Thiocyanation of aromaticcompounds has been investigated using the combination of 1-chloro-1,2-benziodoxol-3-(1H)-one (1) and (trimethylsilyl)isothiocyanate (TMSNCS). The reaction with electron rich aromaticcompounds proceeded smoothly to provide the thiocyanated products in high yield, while electron deficient heteroaromaticcompounds were not suitable for this reaction. In these reactions, the regioselectivity
Bumagin, N. A.; Nikitina, A. F.; Beletskaya, I. P., Russian Journal of Organic Chemistry, 1994, vol. 30, # 10, p. 1619 - 1629
作者:Bumagin, N. A.、Nikitina, A. F.、Beletskaya, I. P.
DOI:——
日期:——
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.
STEFAN, KLAUS-PETER;SCHUHMANN, WOLFGANG;PARLAR, HARUN;KORTE, FRIEDHELM, CHEM. BER., 122,(1989) N, C. 169-174