“…Alkylative cleavage of cyclic ethers in the presence of Lewis acid is abundantly illustrated in the literature. ,− Much less is known however about the factors which allow fragmentation/alkylation tandem with C−C bond formation. , To check the feasibility of the 9-BBN triflate mediated alkylation in the absence of the imidazoline moiety, in a model reaction, lithiated diphenylmethane was treated under standard conditions with 9-BBN triflate, and the alkylated product 31 was obtained 18e in 60% yield (Scheme ). 8 …”
Section: Resultsmentioning
confidence: 99%
“…Surprisingly, by choosing compound 8b and a considerably stronger Lewis acid such as BF 3 ·Et 2 O, the reaction afforded only trace amounts of alkylated product 22 under standard conditions (−100 °C, 3 min). Other boron Lewis acids, such as Et 3 B, which cleaved efficiently cyclic etheral bonds in the presence of NaBH 4 , afforded under the aforementioned conditions (−100 °C, 3 min) a low conversion of 8b to an inextricable mixture of N - and C -ethylated products. No formation of the desired alcohol 22 was observed.…”
Alkylative ring opening of tetrahydrofuran in the presence of 9-BBN triflate is studied. Dianions
derived from C
2
symmetric imidazolines induce excellent to modest acyclic diastereoselectivity to
form quaternary benzylic centers, using the 9-BBN triflate/THF system or methyl iodide as
electrophiles. The direction of the stereoinduction is consistent in both cases. Absolute configuration
for the newly created stereogenic center was established by chemical correlation. Low-temperature
NMR studies of the dilithiated intermediates 42 and 43 suggest the presence of N- and C-metalated
compounds, where the metal-bearing benzylic carbon is sp3 hybridized.
“…Alkylative cleavage of cyclic ethers in the presence of Lewis acid is abundantly illustrated in the literature. ,− Much less is known however about the factors which allow fragmentation/alkylation tandem with C−C bond formation. , To check the feasibility of the 9-BBN triflate mediated alkylation in the absence of the imidazoline moiety, in a model reaction, lithiated diphenylmethane was treated under standard conditions with 9-BBN triflate, and the alkylated product 31 was obtained 18e in 60% yield (Scheme ). 8 …”
Section: Resultsmentioning
confidence: 99%
“…Surprisingly, by choosing compound 8b and a considerably stronger Lewis acid such as BF 3 ·Et 2 O, the reaction afforded only trace amounts of alkylated product 22 under standard conditions (−100 °C, 3 min). Other boron Lewis acids, such as Et 3 B, which cleaved efficiently cyclic etheral bonds in the presence of NaBH 4 , afforded under the aforementioned conditions (−100 °C, 3 min) a low conversion of 8b to an inextricable mixture of N - and C -ethylated products. No formation of the desired alcohol 22 was observed.…”
Alkylative ring opening of tetrahydrofuran in the presence of 9-BBN triflate is studied. Dianions
derived from C
2
symmetric imidazolines induce excellent to modest acyclic diastereoselectivity to
form quaternary benzylic centers, using the 9-BBN triflate/THF system or methyl iodide as
electrophiles. The direction of the stereoinduction is consistent in both cases. Absolute configuration
for the newly created stereogenic center was established by chemical correlation. Low-temperature
NMR studies of the dilithiated intermediates 42 and 43 suggest the presence of N- and C-metalated
compounds, where the metal-bearing benzylic carbon is sp3 hybridized.
“…Lithium triethylborohydride cleaves epoxides easily,19 and lithium tri-tert-butoxyaluminohydride in the presence of triethylboron rapidly opens the THF ring at 25 °C. 20 No analogous ethers were formed in any of our other experiments, however, and no formation of 1-butanol could be detected.…”
Figure 2. lH NMR spectra (100 MHz) of ethylmethylsulfonium 3,4-dihydro-l,4-dioxo-3-(phenylimino)-2(lif)-naphthylenylide (3) in Me2SO-de at various temperatures: (a) 32 °C, (b) 60 °C, (c) 80 °C, (d) 100 °C.
“…Compound 3 originates from the splitting of the Al–O–Al unit promoted by the BH 3 ·THF complex and the reductive ring-opening reaction of two THF molecules to form O n Bu substituent groups. In this regard, boranes B x H y are known to promote THF ring-opening reactions at high temperatures (BH 3 ) or using a mixture of B 2 H 6 /LiAlH 4 at ambient temperature …”
The reaction of metalloxanes [{LM(OH)}(μ-O)] [M = Al (1), Ga (2); L = CH{CMe(NAr)}, Ar = 2,4,6-MeCH, Me = methyl] with an excess of BH·D (D = tetrahydrofuran (THF), SMe) affords annular metallaborate systems achieved through M-O-M cleavage. Compound 1 led exclusively to the formation of eight-membered ring systems [{LAl(μ-O){B(OBu)}(μ-O)}] (3) and [{LAl(μ-O)(BH)(μ-O)}] (6), while for 2 the unprecedented six-membered ring systems [{(LGa)(μ-O)}(μ-O){B(OBu)}] (4) and [(LGa)(μ-O){(BOBu)(μ-O)}] (5) were observed. The use of BH·THF with 1 and 2 led to the concomitant THF ring-opening reaction, while with BH·SMe in THF no such reaction was observed. The metallaborates [LAl{OB(pinacol)}(OH)] (7) and [{LGa(OB(pinacol))}(μ-O)] (8) were synthesized from pinacolborane and the corresponding metalloxane, providing structural evidence that supports the reaction pathways proposed for the formation of 3-6. Density functional theory studies were performed on 3-5 to assess the effect of the metal exchange between aluminum and gallium atoms on the energy of the general ring structures.
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