The reaction of 1-silylcyclopropyl anions with dichloromethyl methyl ether: the efficient synthesis of cyclopropyl silyl ketones via cyclopropylidene derivatives

Progress in the Synthesis and Transformations of Alkylidenecyclopropanes and Alkylidenecyclobutanes

“…Elimination of lithium chloride from the resulting carbenoid 148 and subsequent or simultaneous 1,2-shift of the silyl group affords the final products 149 (Scheme 39). 48,49 An enantioselective organocatalytic approach to alkylidenecyclopropanes has been developed using the Michael addition to nitroalkenes 151 of a cyclopropane-containing aldehyde 150, obtained by a Kulinkovich reaction of ethyl 3,3-diethoxypropanoate and subsequent acetylation. The reaction requires the use of an enantiopure diphenylprolinol silyl ether 152 and an acid cocatalyst, 4-nitrophenol, to furnish acceptable yields and excellent enantiomeric excesses of ACP 153 (Scheme 40).…”

“…56 Scheme 39. Synthesis of Silyl-Substituted ACPs 48,49 Scheme 40. Enantioselective Organocatalytic Approach to ACPs 50 Scheme 41.…”

“…The results of the three-step one-pot procedure starting from 254 are summarized in Scheme 70 (see also Scheme 39). 49,88 The Brønsted acid NH 4 Cl catalyzes a chemoselective hydration and hydroamination of (dicyclopropylmethylene)cyclopropane ( 257) by H 2 O and basic amines, respectively, with conservation of all three cyclopropane rings (Scheme 71). 89 No conversion of 257 was accomplished with benzyl alcohol or amines such as aniline or secondary dibenzylamine.…”

“…In the proposed reaction mechanism, the carbene 147 , derived from the reaction of dichloromethyl methyl ether with butyllithium, reacts with the cyclopropyllithium derivative 146 . Elimination of lithium chloride from the resulting carbenoid 148 and subsequent or simultaneous 1,2-shift of the silyl group affords the final products 149 (Scheme ). , …”

“…Various electrophiles were used to trap methylenecyclopropanes 149 in situ without isolation. The results of the three-step one-pot procedure starting from 254 are summarized in Scheme (see also Scheme ). , …”