[52186-89-7] · C24H24BF4O2P · [1-(Ethoxycarbonyl)cyclopropyl]triphenylphosphonium Tetrafluoroborate · (MW 462.24)
(used in annulation reactions with nucleophile-carbonyl pairs such as anions derived from b-dicarbonyls and imides)
Physical Data: mp 179-181 °C.
Solubility: sol chloroform; slightly sol DMSO, DMF, HMPT; insol diethyl ether.
Form Supplied in: white, nonhygroscopic crystalline solid.
Preparative Methods: prepared in 80% yield by treating commercially available Cyclopropyltriphenylphosphonium Bromide sequentially with Lithium Diisopropylamide and Ethyl Chloroformate, followed by counterion exchange using sodium fluoroborate.1
Purification: recrystallization from chloroform-ether.
The title reagent (1) is a geminally activated cyclopropane which reacts with a variety of carbonyl-containing carbon nucleophiles to afford carbocyclic products. This annulation process has been accomplished using anions derived from 1,3-diketones (eq 1),1 b-keto esters (eq 2),1,2 b-keto aldehydes (eq 3),3 and b-keto phosphonates4 to afford perhydroindans, spiranes, and cyclopentene-1-carboxylates. These reactions are most commonly conducted at 25 °C in HMPA but examples using DMSO (25 °C), DMF (25 °C), and THF (65 °C) as solvent have also been reported. The reactions involve ring opening of the cyclopropane followed by an intramolecular Wittig reaction of the resulting intermediate-stabilized phosphorane. The Wittig reaction occurs at the most reactive carbonyl group when dicarbonyl compounds are used (eqs 2, 3).
This annulation procedure has been used to prepare terpenoid materials, including spirovetivanes, steroids, and insect growth regulators.3-5
Anions derived from imides (eq 4)6 -8 and carboxylic acids (eq 5)9 react with (1) to afford dihydropyrroles and dihydrofurans. These processes have been used in the synthesis of pyrrolizidine and furoquinoline alkaloids.6,9 Monothioimides give mixtures of products derived from Wittig reaction at both the carbonyl and thiocarbonyl groups.6
Heterocycles such as (2)-(4) have also been prepared from (1) and the appropriate nitrogen-, oxygen-, or sulfur-centered anions.1,10 Intermediate stabilized phosphoranes have been characterized in several instances.8,10
[1-(Methoxycarbonyl)cyclopropyl]triphenylphosphonium tetrafluoroborate [52186-91-1]1 has seen little use and gave inferior yields in reactions with imide anions.8 [1-(Ethoxycarbonyl)cyclobutyl]triphenylphosphonium tetrafluoroborate fails to give annulation products with the sodium salt of ethyl acetoacetate.1 [1-(Phenylthio)cyclopropyl]triphenylphosphonium tetrafluoroborate [58992-26-0] has been shown to undergo some annulation reactions related to those reported for (1).11 One example is shown in eq 6.6
David J. Hart
The Ohio State University, Columbus, OH, USA