β-Trimethylsilyl Cyclopropylcarbenes

Creary, Xavier; Butchko, Mark A.

doi:10.1021/jo001112b

Cited by 21 publications

(4 citation statements)

References 26 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Thus, we turned our attention to a silyl group, which is known to undergo a facile 1,2-migration to electron-deficient centers. Despite the well-known 1,2-Si migration to cationic centers,9,10 only little attention was devoted to 1,2-Si shifts to free-11 or metal-stabilized carbenes,12 especially with a focus on synthetic significance. Besides, scarce studies on migratory aptitudes in these systems have been reported 11,12…”

Section: Resultsmentioning

confidence: 99%

Computation-Guided Development of Au-Catalyzed Cycloisomerizations Proceeding via 1,2-Si or 1,2-H Migrations: Regiodivergent Synthesis of Silylfurans

et al. 2010

View full text Add to dashboard Cite

A novel highly efficient regiodivergent Au-catalyzed cycloisomerization of allenyl-and homopropargylic ketones into synthetically valuable 2-and 3-silylfurans has been designed with the aid of the DFT calculations. This cascade transformation features 1,2-Si-or 1,2-H migrations in a common Au-carbene intermediate. Both experimental and computational results clearly indicate that the 1,2-Si migration is kinetically favored over the 1,2-shifts of H, alkyl, and aryl groups in the β-Si-substituted Au-carbenes. In addition, experimental results on the Au(I)-catalyzed cycloisomerization of homopropargylic ketones demonstrated that counterion and solvent effects could reverse the above migratory preference. The DFT calculations provided a rationale for this 1,2-migration regiodivergency. Thus, in the case of AuSbF 6 − , DFT-simulated reaction proceeds through the initial propargyl-allenyl isomerization followed by the cyclization into the Au-carbene intermediate with the exclusive formation of 1,2-Si migration products and solvent effects cannot affect this regioselectivity. However, in the case of TfO − -counterion, reaction occurs via the initial 5-endo-dig cyclization to give cyclic furyl-Au intermediate. In the case of nonpolar solvents, subsequent ipso-protiodeauration of the latter is kinetically more favorable than the generation of the common Au-carbene intermediate and leads to the formation of formal 1,2-H migration products. In contrast, when polar solvent is employed in this DFT-simulated reaction, β-to-Au protonation of the furyl-Au species to give Au-carbene intermediate competes with the ipso-protiodeauration. Subsequent dissociation of the triflate ligand in this carbene in polar media due to efficient solvation of charged intermediates facilitates formation of the 1,2-Si shift products. The above results of DFT calculations were validated by the experimental data. The present study demonstrates that the DFT calculations could efficiently support experimental results, providing guidance for rational design of new catalytic transformations.

show abstract

Section: Resultsmentioning

confidence: 99%

Computation-Guided Development of Au-Catalyzed Cycloisomerizations Proceeding via 1,2-Si or 1,2-H Migrations: Regiodivergent Synthesis of Silylfurans

et al. 2010

View full text Add to dashboard Cite

show abstract

“…Hyperconjugative interactionsdefined as stereoelectronic interactions involving at least one σ orbitalare ubiquitous in chemistry and have profound effects on reactivity and conformational equilibria. − A prominent example is the β-effect of silicon (or β-Si effect), where a R 3 Si substituent stabilizes positive charge at a position β to the silicon group, manifesting extraordinary rate accelerations, − activation of typically inert functionalities , (e.g., C–H bonds), control over selectivity, − and the isolation of typically high energy carbocation − and carbene , species.…”

Section: Introductionmentioning

confidence: 99%

Generality and Strength of Transition Metal β-Effects

2018

View full text Add to dashboard Cite

Using computation, we examine the generality and strength of β-effects from transition metal centers on β-elimination. In particular, we find that a β-Pd(II) substituent imparts over twice the stabilization to a carbocation as a Si substituent, representative of the well-known β-silicon effect. We established efficient and practical computational parameters to investigate the σσ conjugation in an experimentally relevant system: N, N-picolinamide vinyl metalacycles with β-substituents that can undergo elimination. We have found that the β-Pd effect depends on the nature of the C substituent (X): This effect is negligible for X = H, Me, OH, and F, but is significant for X = Cl, Br, and I. We have also extended these studies to the β-effect in N, N-picolinamide vinyl metalacycles with β-substituents of other transition metals-Fe(II), Ru(II), Os(II), Co(III), Rh(III), Ir(III), Ni(II), Pd(II), Pt(II), Cu(III), Ag(III), and Au(III). We found that the electronegativity of the metals correlates reasonably well with the relative β-effects, with first-row transition metals exerting the strongest influence. Overall, it is our anticipation that a more profound appreciation of transition metal β-effects will facilitate the design of novel reactions, including new variants of transition metal catalyzed C-H functionalization.

show abstract

“…C. Computational Studies. Theoretical studies on the effect of bystander substituents on the reaction of carbenes have gained considerable attention. ,8b, Such studies have often been employed to rationalize the experimentally observed product distribution. Even though the effect of substituents on the mode of rearrangement in many cyclic carbenes has been studied, analogous studies with acyclic carbenes are not widely available.…”

Section: Resultsmentioning

confidence: 99%

“…Currently there is limited information available about the effect of β-heteroatoms on carbene reactivity. 1a,c, Specifically, only a few examples of (putative) β-hydroxycarbenes have been reported to date. , An acyclic β-hydroxycarbene, HOCH 2 −C−CH 3 , as generated thermally from a diazirine precursor, proceeds to rearrange exclusively via 1,2-H migration to generate propanal (Scheme a) 9a. Tomioka and Nunome reported the photochemical generation of a phenyl-substituted β-hydroxycarbene from the corresponding diazo precursor (Scheme b), and they observed an experimental 4:1 preference for alkyl (R) migration over O−H insertion and with no 1,3-C−H insertion 9b…”

Section: Introductionmentioning

confidence: 99%

Rearrangement Pathways of 2-Hydroxy-2-methylpropylidene: An Experimental and Computational Study

Farlow

Thamattoor²,

Sunoj³

et al. 2002

J. Org. Chem.

View full text Add to dashboard Cite

Photolysis of exo-2-(1a,9b-dihydro-1H-cyclopropa[l]phenanthren-1-yl)propan-2-ol in benzene-d(6) afforded phenanthrene and the beta-hydroxycarbene intermediate 2-hydroxy-2-methylpropylidene. The carbene showed an overwhelming preference for 1,2-methyl migration as evident from the formation of 2-butanone as the major product via the enol 2-hydroxy-2-butene. Also produced, albeit in smaller amounts, were 1-methylcyclopropanol and 2,2-dimethyloxirane from intramolecular insertion into the C-H and O-H bonds, respectively. These results stand in sharp contrast to the intramolecular reactions of simple alkylcarbenes which usually prefer insertion into C-H bonds over 1,2-alkyl migrations. Calculations at the B3LYP/6-311+G//B3LYP/6-31G level of theory give a lower activation barrier for 1,2-methyl migration leading to the eventual formation of 2-butanone than for the other two pathways. The lower activation energy for methyl migration, relative to C-H and O-H insertions, strongly supports the observed experimental product distribution of the carbene. The parent carbene exists in three distinct conformations, each with stabilizing interactions between the adjacent bonds and the empty p orbital and the filled sp(2) orbital of the carbene center. The most stable conformer is perfectly poised for a 1,2-methyl migration as the C-CH(3) group is involved in a hyperconjugative interaction with the empty p orbital and the O-H bond is simultaneously interacting with the sp(2) lone pair of the carbene.

show abstract

β-Trimethylsilyl Cyclopropylcarbenes

Cited by 21 publications

References 26 publications

Computation-Guided Development of Au-Catalyzed Cycloisomerizations Proceeding via 1,2-Si or 1,2-H Migrations: Regiodivergent Synthesis of Silylfurans

Computation-Guided Development of Au-Catalyzed Cycloisomerizations Proceeding via 1,2-Si or 1,2-H Migrations: Regiodivergent Synthesis of Silylfurans

Generality and Strength of Transition Metal β-Effects

Rearrangement Pathways of 2-Hydroxy-2-methylpropylidene: An Experimental and Computational Study

Contact Info

Product

Resources

About