Treatment of 1-chlorocyclobutyl p-tolyl sulfoxides with Grignard reagents such as ethylmagnesium chloride, isopropylmagnesium chloride, and cyclopentylmagnesium chloride in THF at low temperature gave cyclobutylmagnesium carbenoids in high yields. The generated magnesium carbenoids were found to be stable at -78°C for at least 30 minutes. The cyclobutylmagnesium carbenoids reacted with several nucleophiles to give multi-substituted cyclobutanes. The reaction of the cyclobutylmagnesium carbenoids with lithium a-sulfonyl carbanions afforded alkylidenecyclobutanes in moderate to good yields.Although cyclobutane skeletal structures are not widely found in natural products, cyclobutane derivatives are quite interesting compounds. Due to high angular and torsional strain, cyclobutanes are fairly reactive under a variety of conditions and often used as versatile intermediates in organic synthesis. 1 Cyclopropanes are another smallring compounds having inherent ring strain comparable to that of cyclobutanes and have been widely studied in organic chemistry; however, the chemistry of cyclobutanes is not fully investigated even now.We have been interested in the chemistry of cyclopropanes, especially cyclopropylmagnesium carbenoids (cyclopropanes bearing magnesium and chlorine atoms at the same carbon) generated from 1-chlorocyclopropyl p-tolyl sulfoxides with Grignard reagents, and many interesting properties of the carbenoids have been unveiled. 2 In continuation of our interest in the chemistry of small-ring magnesium carbenoids, we recently started to investigate the generation, property, and synthetic uses of cyclobutylmagnesium carbenoids, which delivered quite interesting results. 3 Thus, as shown in Scheme 1, treatment of 1-chlorocyclobutyl p-tolyl sulfoxides 1 with Grignard reagents (R 2 MgCl) in THF at low temperature afforded cyclobutylmagnesium carbenoids 2 in high yields via the sulfoxidemagnesium exchange reaction. 4 The generated cyclobutylmagnesium carbenoids 2 were found to be stable at -78°C for at least 30 minutes. When this reaction was carried out with excess R 2 MgCl, carbenoids 2 were alkylated with the Grignard reagents to give the alkylated cyclobutylmagnesium chloride intermediates 3, which could be trapped with electrophiles to give multi-substituted cyclobutanes 4 in moderate to good yields. Cyclobutylmagnesium carbenoids 2 were proved to be reactive with some alkyllithiums and N-lithioarylamines to give cyclobutanes 5. The reaction of 2 with lithium a-sulfonyl carbanions gave alkylidenecyclobutanes 6 in moderate to good yields. Details of the aforementioned results are reported in this paper.
Scheme 1
Synthesis of 1-Chlorocyclobutyl p-Tolyl SulfoxidesThree 1-chlorocyclobutyl p-tolyl sulfoxides 1a-c were selected, which are the precursors for the generation of cyclobutylmagnesium carbenoids 2, and synthesized them as follows (Scheme 2). Alkylation of the two hydroxy groups of known diol 7 5 with 3-phenylpropyl bromide followed by catalytic hydrogenation and oxidation with IBX in DMSO gave cyclob...
Coupling Reaction of Magnesium Alkylidene Carbenoids with α-Sulfonylallyllithiums: An Efficient Route to Multi-Substituted Vinylallenes. -The method allows a ready access to various highly unsaturated title compounds. -(KIMURA, T.; KOBAYASHI, G.; ISHIGAKI, M.; INUMURA, M.; SAKURADA, J.; SATOH*, T.; Synthesis 2012, 23, 3623-3632, http://dx.doi.org/10.1055/s-0032-1317507 ; Dep. Chem., Fac. Sci., Sci. Univ. Tokyo, Shinjuku, Tokyo 162, Japan; Eng.) -Mais 13-035
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