7 research outputs found
Reactions promoted by hypervalent iodine reagents and boron Lewis acids
Understanding the role of boranes in hypervalent iodine chemistry will open up new reactivities which can be utilised in organic synthesis. Due to similar reactivities, Îť3-iodanes have presented themselves as viable alternatives for many transformations dominated by transition metals whilst mitigating some of the associated drawbacks of metal systems. As showcased by recent reports, boranes can adopt a dual role in hypervalent iodine chemistry that surpasses mere activation of the hypervalent iodine reagent. Increased efforts to harness this potential with diverse boranes will uncover exciting reactivity with high applicability across various disciplines including adoption in the pharmaceutical sciences. This review will be relevant to the wider synthetic community including organic, inorganic, materials, and medicinal chemists due to the versatility of hypervalent iodine chemistry especially in combination with borane activation or participation. We aim to highlight the development of hypervalent iodine compounds including their structure, bonding, synthesis and utility in metal-free organic synthesis in combination with Lewis acidic boranes
Fluorocyclisation via I(I)/I(III) catalysis: a concise route to fluorinated oxazolines
Herein, we describe a catalytic fluorooxygenation of readily accessible N-allylcarboxamides via an I(I)/I(III) manifold to generate 2-oxazolines containing a fluoromethyl group. Catalysis is conditional on the oxidation competence of SelectfluorÂŽ, whilst HF serves as both a fluoride source and Brønsted acid activator. The C(sp3)âF bond of the mono-fluoromethyl unit and the C(sp3)âO bond of the ring are aligned in a synclinal relationship thereby engaging in stabilising hyperconjugative interactions with vicinal, electron-rich Ď-bonds (ĎCâCâĎ*CâF and ĎCâHâĎ*CâO). This manifestation of the stereoelectronic gauche effect was established by X-ray crystallographic analysis of a representative example. Given the importance of fluorine in drug discovery, its ability to modulate conformation, and the prevalence of the 2-oxazoline scaffold in Nature, this strategy provides a rapid entry into an important bioisostere class
Deconstructing the Catalytic, <i>Vicinal</i> Difluorination of Alkenes: HF-Free Synthesis and Structural Study of <i>p</i>âTolIF<sub>2</sub>
Recently, contemporaneous strategies
to achieve the <i>vicinal</i> difluorination of alkenes
via an IÂ(I)/IÂ(III) catalysis manifold
were independently reported by this laboratory and by Jacobsen and
co-workers. Both strategies proceed through a transient ArIÂ(III)ÂF<sub>2</sub> species generated by oxidation of the ArI catalyst. Herein,
an efficient synthesis of <i>p</i>-TolIF<sub>2</sub> from <i>p</i>-TolI and Selectfluor is presented, together with a crystallographic
and spectroscopic study. To mitigate safety concerns and simplify
reaction execution, an HF-free protocol was devised employing CsF
as a substitute fluoride source. The study provides insight into the
initial IÂ(I)âIÂ(III) oxidation stage of the catalytic protocol
using Selectfluor
The SulfurâFluorine <i>Gauche</i> Effect in Coinage-Metal Complexes: Augmenting Conformational Equilibria by Complexation
Controlling
the rotation about unhindered CÂ(sp<sup>3</sup>)âCÂ(sp<sup>3</sup>) bonds by simple structural changes has obvious benefits
in molecular design. While the avoidance of nonbonding interactions
remains one of the cornerstones of acyclic conformational control,
stabilizing stereoelectronic effects have the added benefit that conformer
populations can be fine-tuned by augmenting or diminishing the central
interaction. Strategies may include adjusting the oxidation state
of a substituent or reversible formation of a complex to modulate
MO levels. In the case of the sulfurâfluorine <i>gauche</i> effect, the propensity of the SâCâCâF motif
to adopt a <i>synclinal</i> arrangement (Ό<sub>FCCS</sub> = 60°), the conformer population distribution of the three
dominant rotamers partitioned by 120° can be biased by oxidation
of the S atom. Motivated by the importance of sulfur-based ligands
in main structural chemistry, the sulfurâfluorine <i>gauche</i> effect was translated to an organometallic paradigm as a potential
tool to achieve structural preorganization. This would allow the influence
of coinage-metal complexation on conformer population to be initially
assessed. The synthesis and characterization of a model goldÂ(I) and
silverÂ(I) metal complex featuring a ligand system containing a freely
rotatable SCCF motif is disclosed. In both complexes, the title stereoelectronic
effect manifests itself in the expected conformation, with the <i>synclinal</i>-<i>endo</i> conformer being preferred.
This was corroborated by X-ray crystallography and DFT analysis, and
the molar fraction of rotamers was extrapolated from a detailed solution-phase
NMR spectroscopic analysis. Complexation was found to reinforce the
sulfurâfluorine <i>gauche</i> effect
The SulfurâFluorine <i>Gauche</i> Effect in Coinage-Metal Complexes: Augmenting Conformational Equilibria by Complexation
Controlling
the rotation about unhindered CÂ(sp<sup>3</sup>)âCÂ(sp<sup>3</sup>) bonds by simple structural changes has obvious benefits
in molecular design. While the avoidance of nonbonding interactions
remains one of the cornerstones of acyclic conformational control,
stabilizing stereoelectronic effects have the added benefit that conformer
populations can be fine-tuned by augmenting or diminishing the central
interaction. Strategies may include adjusting the oxidation state
of a substituent or reversible formation of a complex to modulate
MO levels. In the case of the sulfurâfluorine <i>gauche</i> effect, the propensity of the SâCâCâF motif
to adopt a <i>synclinal</i> arrangement (Ό<sub>FCCS</sub> = 60°), the conformer population distribution of the three
dominant rotamers partitioned by 120° can be biased by oxidation
of the S atom. Motivated by the importance of sulfur-based ligands
in main structural chemistry, the sulfurâfluorine <i>gauche</i> effect was translated to an organometallic paradigm as a potential
tool to achieve structural preorganization. This would allow the influence
of coinage-metal complexation on conformer population to be initially
assessed. The synthesis and characterization of a model goldÂ(I) and
silverÂ(I) metal complex featuring a ligand system containing a freely
rotatable SCCF motif is disclosed. In both complexes, the title stereoelectronic
effect manifests itself in the expected conformation, with the <i>synclinal</i>-<i>endo</i> conformer being preferred.
This was corroborated by X-ray crystallography and DFT analysis, and
the molar fraction of rotamers was extrapolated from a detailed solution-phase
NMR spectroscopic analysis. Complexation was found to reinforce the
sulfurâfluorine <i>gauche</i> effect
The SulfurâFluorine <i>Gauche</i> Effect in Coinage-Metal Complexes: Augmenting Conformational Equilibria by Complexation
Controlling
the rotation about unhindered CÂ(sp<sup>3</sup>)âCÂ(sp<sup>3</sup>) bonds by simple structural changes has obvious benefits
in molecular design. While the avoidance of nonbonding interactions
remains one of the cornerstones of acyclic conformational control,
stabilizing stereoelectronic effects have the added benefit that conformer
populations can be fine-tuned by augmenting or diminishing the central
interaction. Strategies may include adjusting the oxidation state
of a substituent or reversible formation of a complex to modulate
MO levels. In the case of the sulfurâfluorine <i>gauche</i> effect, the propensity of the SâCâCâF motif
to adopt a <i>synclinal</i> arrangement (Ό<sub>FCCS</sub> = 60°), the conformer population distribution of the three
dominant rotamers partitioned by 120° can be biased by oxidation
of the S atom. Motivated by the importance of sulfur-based ligands
in main structural chemistry, the sulfurâfluorine <i>gauche</i> effect was translated to an organometallic paradigm as a potential
tool to achieve structural preorganization. This would allow the influence
of coinage-metal complexation on conformer population to be initially
assessed. The synthesis and characterization of a model goldÂ(I) and
silverÂ(I) metal complex featuring a ligand system containing a freely
rotatable SCCF motif is disclosed. In both complexes, the title stereoelectronic
effect manifests itself in the expected conformation, with the <i>synclinal</i>-<i>endo</i> conformer being preferred.
This was corroborated by X-ray crystallography and DFT analysis, and
the molar fraction of rotamers was extrapolated from a detailed solution-phase
NMR spectroscopic analysis. Complexation was found to reinforce the
sulfurâfluorine <i>gauche</i> effect