Reactions of gem-dibromo compounds with trialkylmagnesate reagents to yield alkylated organomagnesium compounds

Chromium-catalyzed cyclopropanation of alkenes with bromoform in the presence of 2,3,5,6-tetramethyl-1,4-bis(trimethylsilyl)-1,4-dihydropyrazine

Chromium-catalyzed cyclopropanation of alkenes with bromoform was achieved to produce the corresponding bromocyclopropanes. In this catalytic cyclopropanation, an organosilicon reductant, 2,3,5,6-tetramethyl-1,4-bis(trimethylsilyl)-1,4-dihydropyrazine (1a), was indispensable for reducing CrCl3(thf)3 to CrCl2(thf)3, as well as for in situ generation of (bromomethylidene)chromium(iii) species from (dibromomethyl)chromium(iii) species. The (bromomethylidene)chromium(iii) species are proposed to react spontaneously with alkenes to give the corresponding bromocyclopropanes. This catalytic cyclopropanation was applied to various olefinic substrates, such as allyl ethers, allyl esters, terminal alkenes, and cyclic alkenes.

Construction of highly sterically hindered 1,1-disilylated terminal alkenes

One direct and efficient procedure for the synthesis of 1,1-disilylated terminal alkenes is demonstrated in this paper. To overcome and rationally utilize the steric hindrance of silyl units, the cationic ruthenium catalyst [CpRu(MeCN)3]+ was found to be effective for Markovnikov hydrosilylation of 1-silyl terminal alkynes with high yields and excellent regioselectivity. Dissimilarities between alkyl and alkoxy silyl units lead to versatile product derivatizations toward a variety of useful building blocks.

Highly functionalized donor-acceptor cyclopropanes applied toward the synthesis of the Melodinus alkaloids

A series of highly substituted vinylcyclopropanes were prepared and examined as reaction partners in a palladium-catalyzed (3 + 2) cycloaddition with nitrostyrenes. Described herein are our efforts to synthesize an elusive 1,1-divinylcyclopropane by several distinct approaches, and to apply surrogates of this fragment toward the synthesis of the Melodinus alkaloids.

Solid state and solution studies of lithium tris(n-butyl)magnesiates stabilised by Lewis donors

Donor complexes of the synthetically important lithium magnesiate LiMg(ⁿBu)₃ have been prepared and characterised.

Sakurai reaction of 3,3-bis(silyl) silyl enol ethers with acetals involving selective desilylation of the geminal bis(silane). Concise synthesis of nematocidal oxylipid

3,3-Bis(silyl) silyl enol ethers have been shown to exhibit predominantly Sakurai reactivity, rather than Mukaiyama aldol reactivity, in their Lewis acid promoted reactions with acetals. Starting from a geminal bis(silyl) moiety consisting of two different silyl groups, such as SiMe(3) and SiMe(2)Ph, the SiMe(3) is selectively eliminated to give monoprotected E- vinylsilyl diols with good to excellent syn-diastereoselectivity. This reaction also underpinned a synthesis of the nematocidal oxylipid from Notheia anomala, demonstrating the attractive bifunctionality of geminal bis(silanes).

One-step preparation of functionalized (E)-vinylsilanes from aldehydes

Functionalized (E)-vinylsilanes have been prepared in one step from a wide range of aldehydes, via a chromium(II)-mediated olefination with novel dihalomethylsilane reagents, in moderate to excellent yields and with excellent stereoselectivity.

Synthesis and structural characterisation of alkali metal complexes of heteroatom-stabilised 1,4- and 1,6-dicarbanions

A straightforward Peterson olefination reaction between either [{(Me(2)PhSi)(3)C}Li(THF)] or in situ-generated [(Me(3)Si)(2){Ph(2)P(BH(3))}CLi(THF)(n)] and paraformaldehyde gives the alkenes (Me(2)PhSi)(2)C[double bond, length as m-dash]CH(2) () and (Me(3)Si){Ph(2)P(BH(3))}C[double bond, length as m-dash]CH(2) (), respectively, in good yield. Ultrasonic treatment of with lithium in THF yields the lithium complex [{(Me(2)PhSi)(2)C(CH(2))}Li(THF)(n)](2) (), which reacts in situ with one equivalent of KOBu(t) in diethyl ether to give the potassium salt [{(Me(2)PhSi)(2)C(CH(2))}K(THF)](2) (). Similarly, ultrasonic treatment of with lithium in THF yields the lithium complex [[{Ph(2)P(BH(3))}(Me(3)Si)C(CH(2))]Li(THF)(3)](2).2THF (). The bis(phosphine-borane) [(Me(3)Si){Me(2)(H(3)B)P}CH(Me(2)Si)(CH(2))](2) () may be prepared by the reaction of [Me(2)P(BH(3))CH(SiMe(3))]Li with half an equivalent of ClSiMe(2)CH(2)CH(2)SiMe(2)Cl in refluxing THF. Metalation of with two equivalents of MeLi in refluxing THF yields the lithium complex [[{Me(2)P(BH(3))}(Me(3)Si)C{(SiMe(2))(CH(2))}]Li(THF)(3)](2) (), whereas metalation with two equivalents of MeK in cold diethyl ether yields the potassium complex [[{Me(2)P(BH(3))}(Me(3)Si)C{(SiMe(2))(CH(2))}](2)K(2)(THF)(4)](infinity) () after recrystallisation. X-Ray crystallography shows that, whereas the lithium complex crystallises as a discrete molecular species, the potassium complexes and crystallise as sheet and chain polymers, respectively.

A New Selective Approach to 1,1-Bis(silyl)-2-arylethenes and 1,1-Bis(silyl)-1,3-butadienes via Sequential Silylative Coupling−Heck Coupling Reactions

A novel selective route to 1,1-bis(silyl)-1-alkenes has been developed. Sequential one-pot silylative coupling exo-cyclization of 1,2-bis(dimethylvinylsiloxy)ethane followed by the reaction with Grignard reagents leads to the desired 1,1-bis(silyl)ethenes, which are then efficiently coupled in the presence of silver nitrate and palladium acetate with aryl or alkenyl idodides to give the corresponding 1,1-bis(silyl)-2-arylethenes or 1,1,4-trisubstituted 1,3-butadienes with high yield.

Highly Alkyl-Selective Addition to Ketones with Magnesium Ate Complexes Derived from Grignard Reagents

A highly efficient alkyl-selective addition to ketones with magnesium ate complexes derived from Grignard reagents and alkyllithiums is described. The nucleophilicity of R in R3MgLi is remarkably increased compared to that of the original RLi or RMgX, while the basicity of R3MgLi is decreased. Furthermore, a highly R-selective addition to ketones is demonstrated using RMe2MgLi in place of R3MgLi. [reaction: see text]