Silicon in organic synthesis. 24. Preparation and selected reactions of functionalized 1-(trimethylsilyl)-substituted cyclopropanes

Abstract

Several methods for preparing bifunctional 1-(trimethylsilyl)-substituted cyclopropanes are described. The methyl bromide 4, available by Simmons-Smith cyclopropanation of 2 and bromination with phosphorus tribromide, is shown to be highly reactive to SN2 displacement and therefore easily transformed into a variety of other derivatives including the phenyl sulfide, phenyl sulfone, nitrile, and phenyl selenide. Ring-closure protocols have been applied to gain access to the triphenylphosphonium salt, phosphonate ester, and carboxaldehyde ( 22). The dimethyl acetal 23 of this aldehyde gives every indication of being an excellent conjunctive reagent as exemplified by its conversion to 24,26, and 30. Reactive anions of type A (X = S02Ph, SPh, SePh, CN) have been generated and in certain cases utilized for additional chemical transformations.Recent reports from these laboratories have described several synthetic2"4 and physical-organic studies5,6 involving silylcyclopropanes. In line with the recent general upsurge of interest in varied applications of organosilicon reagents,7 the boundaries of our previously limited knowledge of silyl-substituted small-ring compounds8 have begun to expand. The efficient preparation of this class of molecules remains, as always, the fundamental cornerstone of their broad-scale utilization. As a small contribution to this technology, we describe here synthetic approaches to a number of functionalized l-(trimethylsilyl)cyclopropanes with thé intent of illustrating their ready accessibility. Some chemical transformations of selected structures are also included to emphasize further

Silyl-substituted cyclopropanes as versatile synthetic reagents

“…Thus, condensation with 125 in the presence of Ti(0) provides 126 Despite the neopentyl nature of the halogen-substituted carbon in 121, the substance enters readily into Sn2 displacement reactions. 56 That this bromide is a respectable electrophilic reagent can be seen in the following. The functional group combination found in 127 has proven useful in the preparation of molecules such as 128, which incorporates allylsilane and acrylonitrile moieties that work in electronic opposition.56 Generally, silver ion-assisted ionizations of gem-dihalocyclopropanes result in disrotatory ring cleavage with formation of an allyl cation whose geometry is dependent on the specific halogen that is abstracted.…”

Lithium Chloride-Mediated Stereoselective Synthesis of Cyclopropanecarboxamides from γ,δ-Epoxy Malonates through a Domino Cyclopropanation/Lactonization/Aminolysis Process

“…Due to the interest in the chemistry of functionalized cyclopropanes, a variety of methods describing the preparation of these strained carbocycles have recently been reported in the literature. − One of the most commonly used approaches is based on intramolecular nucleophilic substitution (S N ) reactions involving the attack of a carbanion-like nucleophile on a pre-existing electrophilic site, these two reaction centers being separated by one carbon atom. While this strategy has been successfully explored with substrate A containing different “X” leaving groups − and also with epoxides of the B type − (Scheme ), the need for the use of strong bases or sensitive organometallic reagents in an anhydrous environment is a serious restriction in terms of its wider application. Furthermore, in many circumstances the availability of the starting materials poses a challenge, the structural diversity is limited to a few examples, and the stereoselectivity related to the resulting substituted cyclopropane is only moderate.…”

Amino-Protecting Groups Subject to Deblocking under Conditions of Nucleophilic Addition to a Michael Acceptor. Structure−Reactivity Studies and Use of the 2-(tert-Butylsulfonyl)-2-propenyloxycarbonyl (Bspoc) Group

“…Alternatively, an appropriate chloroformate was treated with p -chloroaniline to give 3 . Known alcohols ( 2 , EWG = SiMe 3 , COOEt, C 6 H 4 NO 2 - p ) were obtained by published methods. The phenylsulfinyl and phenylsulfonyl alcohols ( 2 , EWG = C 6 H 5 SO, C 6 H 5 SO 2 ) were readily obtained from sulfide alcohol 4 5 by m -chloroperbenzoic acid (MCPBA) oxidation.…”