Synthesis of 2′,3′-dideoxy-3′,3′-difluoro and 2′,3′-dideoxy-2′,2′-difluoro-pyranosyl nucleosides analogues of gemcitabine

Influence of the Element and Substituent Effects on the Reactivity of Catching Reactions of Difluorocarbene by Benzene-Bridged and Group-13/Group-15-Based Frustrated Lewis Pairs

The trapping reactions of CF₂ by benzene-bridged Group-13/P-based and B/Group-15-based frustrated Lewis pairs (FLPs) have been computationally investigated based on density functional theory. Interestingly, our theoretical calculations predict that the capture of CF₂ by all five Group-13/P-based FLPs is energetically feasible. However, in the B/Group-15-based FLPs, only the phosphorus-based B/P-FLP can trap CF₂ from kinetic and thermodynamical viewpoints. According to the analyses of the activation strain model, it can be known that the atomic radius of the G15 element (Lewis base) of benzene-bridged B/Group-15-FLP plays an important role in controlling the reactivity of the CF₂ catching reactions, whereas the atomic radius of the Group-13 center (Lewis acid) does not play a role in influencing the activation barrier of these CF₂ catching reactions. Our theoretical findings based on sophisticated methods suggest that the forward bonding is the FLP-to-CF₂ interaction, the LP (Group-15-donor) → vacant p-π-orbital (CF₂), which was quantitatively proved to be strong in such present CF₂ catching reactions. However, the back bonding is the CF₂-to-FLP interaction, the empty σ-orbital (Group-13-acceptor) ← sp²-σ-orbital (CF₂), which was verified to be relatively weak. Our theoretical pieces of evidence reveal that the stronger electron-donating ability of the substituents is attached to the Lewis basic center and can make the reaction barrier of the benzene-bridged Group-13/Group-15-based FLP-related compound catching CF₂ smaller and more exothermic.

Synthesis of locked pyranosyl nucleic acid (LpNA)

A new locked pyranosyl nucleoside was synthesized by phenylsulfinyl-assisted chemistry. The novel building block was inserted into oligonucleotides and provides new insight on conformational restricted pyranosyl nucleosides on duplex formation.

Difluorophenylsulfanylmethyl Radical and Difluoromethylene Diradical Synthons: gem-Difluoromethylene Building Block

Bromodifluorophenylsulfanylmethane has been demonstrated to be a highly versatile gem-difluoromethylene (CF2) building block via the reaction of difluorophenylsulfanylmethyl radical with olefins. gem-Difluoroalkenes and products containing a midchain CF2 group and with manipulatable functionality can be readily synthesized. The first example of a gem-difluoromethylene radical synthon is also reported.

Highly-functionalised difluorinated (hydroxymethyl)conduritol analogues via the Diels-Alder reactions of a difluorinated dienophile

A difluorodienophile, synthesised using a Stille coupling reaction underwent tin(iv)-catalysed cycloaddition with three furans to afford oxa[2.2.1]bicycloheptenes in good yield. Reduction of ester and carbamate carbonyl groups and diol protection as the acetonide set the stage for palladium-catalysed hydrostannylation in two cases. Treatment of the stannanes with methyllithium triggered ring-opening to afford highly-functionalised difluorinated cyclohexenols which could be deprotected to afford (hydroxymethyl)conduritol analogues.