A surprising steric effect on a tandem cycloaddition/ring-opening reaction : rapid syntheses of difluorinated analogues of (hydroxymethyl)conduritols

Difluorinated analogues of (hydroxymethyl)conduritols can be synthesised from selected furans and a difluorinated dienophile in two reaction steps

Highly-functionalised difluorinated cyclohexane polyols via the Diels–Alder reaction : regiochemical control via the phenylsulfonyl group

A difluorinated dienophile underwent cycloaddition reactions with a range of furans to afford cycloadducts whichcould be processed regio- and stereoselectively via episulfonium ions, generated by the reaction between their alkenyl groups and phenylsulfenyl chloride. The oxabicyclic products were oxidised to the phenylsulfonyl level and ring opened via E1CB or reductive desulfonative pathways to afford, ultimately, difluorinated cyclohexene or cyclohexane polyols

Synthesis and transformation of difluorinated Diels-Alder cycloadducts

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Synthesis and transformation of difluorinated Diels-Alder cycloadducts

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Synthesis and transformation of diflourinated diels-alder cycloadducts

This thesis describes the synthesis of highly substituted geminally difluorinated cyclohexenols based on Diels-Alder reactions between a difluorinated dienophile and furans (furan, 2-methyl and 2,3-dimenthyl) in presence of stannic chloride. The dienophile was synthesised in two different ways: a literature procedure, starting from the commercially available trifluoroethanol and new route involving an organometallic reagent.;Sulphur electrophile chemistry applied to the endo and exo cycloadducts gained stereo- and regio- control completely. Full protection of the free hydroxyl group was required before two different ring-opening strategies could be implemented: a carbanionic and a reductive method were attempted to ring-open the 7-oxabicyclo[2.2.1]heptenyl system. The scope of these methodologies was investigated with furan, 2-methyl and 2,3-dimethyl furan cycloadducts. When a stoichiometric amount of the Lewis acid (stannic chloride) was used in the cycloaddition with furan, an interesting bicyclic carbonate was afforded. To understand the mechanism of the reaction and the role of the Lewis acid in binding the cycloadduct, crystals were grown and an interesting complex was obtained.;Useful vinyl bromide products (endo and carbonate) were generated by cycloaddition between the difluorinated alkenoate and 3-bromofuran in the presence of 1.0 equivalents of tin tetrachloride. Suzuki coupling reaction of endoadduct with phenylboronic acid was carried out under Leadbeater's aqueous microwave conditions. Finally, dihydroxylation of the ring opened products and deprotections of the protected hydroxyl groups delivered the required gem- difluorinated polyhydroxy cyclohexane allowing for the first time the synthesis of cyclitol analogues via Diels-Alder reaction

CCDC 229971: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures

CCDC 229969: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures

CCDC 229970: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures

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

Basic and reductive sulfone-directed ring-opening reactions of difluorinated oxa[2.2.1]bicycloheptanes

Phenylsulfenyl chloride reacts with racemic endo Diels-Alder adduct 4 (DEC ) CONEt2) to afford lactone 8, which can be reduced and protected in a series of high-yielding steps. Key sulfone 10 can be ring opened under strong base conditions to afford vinyl sulfone 11. Attempted desulfonation resulted in the formation of a monofluoroalkene, but a direct desulfonation/eliminative ring opening with strain relief delivered highly functionalized monocyclic species 16