“…Intramolecular hydride transfers in an alkane chain with transition states of these ring sizes are well documented. , Other ring sizes would be strained and higher in energy, accounting for the absence of the fragmentation process in 3 and 4 b , c , and f . Indeed, the reaction pathway presently proposed for our carboranes is quite analogous to that suggested some time ago to account for the results of protonation of certain cyclic enones carrying a trialkylstannylated side chain (Scheme ), except that the departure of the stannyl substituent probably requires nucleophilic assistance. 8 A Previously Reported 33 Intramolecular Hydride Transfer Combined with Grob Fragmentation …”
Section: Discussionsupporting
confidence: 56%
“…The authors thank Ms. Brook K. McConnell, Dr. Magdalena Kvíčalová, Mr. Derek G. Leopold, and Mr. Damian B. Sowers for technical assistance. We are grateful to Prof. Scott D. Rychnovsky (University of California at Irvine) for bringing ref to our attention.…”
In solvolysis of alkyl halides Hal-(CH(2))(n)-C(BCH(3))(11)(-) (n = 2, 5, 6, but not 3, 4, or 7) and protonation of alkenes CH(2)=CH-(CH(2))(n)(-)(2)-C(BCH(3))(11)(-) (n = 3, 6, 7, but not 4 or 5) carrying the icosahedral electrofuge -C(BCH(3))(11)(-) attached through its cage carbon atom, generation of incipient positive charge on C(alpha) (as shown in Scheme 1 in the article) leads to simultaneous cleavage of the C(beta)-C(BCH(3))(11)(-) bond. The products are a C(alpha)=C(beta) alkene and a postulated intermediate C(+)(BCH(3))(11)(-) <--> C(BCH(3))(11), trapped as the adduct Nu-C(BCH(3))(11)(-) by one of the nucleophiles (Nu(-)) present. The reaction kinetics is E1, first order in the haloalkylcarborane and zero order in [Nu(-)], and the elimination appears to be concerted, as in the usual E2 mechanism. The process is best viewed as a Grob fragmentation. The loss of the longer chains involves intrachain hydride transfer from the C(alpha)-H bond to an incipient carbocation on C(delta)(') or C(epsilon)(') via a five- or six-membered cyclic transition state, respectively. The electronic structure of the postulated intermediate is believed to lie between those of a nonclassical carbonium ylide C(+)(BCH(3))(11)(-) and a carbenoid C(BCH(3))(11) whose electronic ground state resembles the S(2) state of ordinary carbenes.
“…Intramolecular hydride transfers in an alkane chain with transition states of these ring sizes are well documented. , Other ring sizes would be strained and higher in energy, accounting for the absence of the fragmentation process in 3 and 4 b , c , and f . Indeed, the reaction pathway presently proposed for our carboranes is quite analogous to that suggested some time ago to account for the results of protonation of certain cyclic enones carrying a trialkylstannylated side chain (Scheme ), except that the departure of the stannyl substituent probably requires nucleophilic assistance. 8 A Previously Reported 33 Intramolecular Hydride Transfer Combined with Grob Fragmentation …”
Section: Discussionsupporting
confidence: 56%
“…The authors thank Ms. Brook K. McConnell, Dr. Magdalena Kvíčalová, Mr. Derek G. Leopold, and Mr. Damian B. Sowers for technical assistance. We are grateful to Prof. Scott D. Rychnovsky (University of California at Irvine) for bringing ref to our attention.…”
In solvolysis of alkyl halides Hal-(CH(2))(n)-C(BCH(3))(11)(-) (n = 2, 5, 6, but not 3, 4, or 7) and protonation of alkenes CH(2)=CH-(CH(2))(n)(-)(2)-C(BCH(3))(11)(-) (n = 3, 6, 7, but not 4 or 5) carrying the icosahedral electrofuge -C(BCH(3))(11)(-) attached through its cage carbon atom, generation of incipient positive charge on C(alpha) (as shown in Scheme 1 in the article) leads to simultaneous cleavage of the C(beta)-C(BCH(3))(11)(-) bond. The products are a C(alpha)=C(beta) alkene and a postulated intermediate C(+)(BCH(3))(11)(-) <--> C(BCH(3))(11), trapped as the adduct Nu-C(BCH(3))(11)(-) by one of the nucleophiles (Nu(-)) present. The reaction kinetics is E1, first order in the haloalkylcarborane and zero order in [Nu(-)], and the elimination appears to be concerted, as in the usual E2 mechanism. The process is best viewed as a Grob fragmentation. The loss of the longer chains involves intrachain hydride transfer from the C(alpha)-H bond to an incipient carbocation on C(delta)(') or C(epsilon)(') via a five- or six-membered cyclic transition state, respectively. The electronic structure of the postulated intermediate is believed to lie between those of a nonclassical carbonium ylide C(+)(BCH(3))(11)(-) and a carbenoid C(BCH(3))(11) whose electronic ground state resembles the S(2) state of ordinary carbenes.
“…Interesting results have been obtained from internal reactions of tetraalkyltins with carbon-centred electrophiles 597 " 599 . Initial results have been achieved with ô-(trimethylstannyl)butyl-or γ-(trimethylstannyl)propyl-substituted enones obtained as in the example 597 of Scheme 10.…”
Well over a decade ago, two reviews were contributed to the
Organic Reactions
series covering substitution and conjugate addition reactions in organocopper chemistry. Their appearance, which highlighted most of the early work in this field, served not only as a source of invaluable references to original literature reports, but also stimulated a vast number of subsequent studies on the properties and uses of organocopper complexes.
The work cited in this chapter, which dates from ca. 1975, concerns in large measure uses of organocopper complexes originating from either catalytic or stoichiometric quantities of a copper(I) halide together with a Grignard (RMgX) or organolithium (RLi) reagent. These combinations form either neutral organocopper reagents RCu (
1
) or copper(I) monoanionic salts R
2
CuM (M = Li or MgX), commonly referred to as “lower‐order” species. The latter
ate
complexes with lithium as gegenion (
2
) are also known as “Gilman reagents” in recognition of their origins. Copper(I) cyanide is also an excellent precursor, affording homogeneous mixtures of lower order cyanocuprates RCu(CN)Li, (
3
), upon treatment with an equivalent of an organolithium. The strength of the CuCN linkage presumably accounts for direct cuprate formation with 1 equivalent of the organolithium, rather than the metathesis that occurs with copper(I) chloride, bromide, or iodide.
While use of reagents (
1
), (
2
) and (
3
) alone can be aptly classified as broad‐based and intense, their importance has further encouraged extensive development of variations on these themes (i.e., their composition and reactivity profiles). Reagents (
1–3
) have been found to be unexpectedly compatible with certain electrophilic additives at low temperatures, which substantially alter their reactivity. Rather than forming (
2
) from 2 equivalents of the same RLi, different organolithiums can be utilized to give R
T
R
R
CuLi, (
4
), conserving potentially valuable RLi. This scenario raises the question of controlling the selectivity of transfer of the desired ligand R
T
rather than the anticipated residual (or “dummy”) group R
R
from copper to electrophilic carbon. Fortunately, many solutions to this problem now exist.
Admixture of 2RLi (or R
T
Li + R
R
Li) with copper(I) cyanide proceeds beyond the stage of (
3
) to ultimately arrive at copper(I) dianionic complexes
5
, the so‐called “higher‐order” cyanocuprates. Undoubtedly it is the cyano ligand, with its π‐acidic nature, which enables copper to accept a third negatively charged ligand. Although reagents (
5
) do not yet share in all of the benefits offered by time in comparison with their lower‐order counterparts, they nicely complement prior art. Moreover, as with species (
1–4
), they continue to evolve, providing the synthetic community with alternatives for highly selective and efficient means of making key carbon–carbon bonds.
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