Immobilisation and application of bifunctional iminophosphorane organocatalysts

Thesis

Bifunctional iminophosphoranes, containing a triaryl-substituted iminophosphorane and bis(3,5- trifluoromethyl)phenyl thiourea on a single enantiomer scaffold are novel asymmetric superbase organocatalysts reported by the Dixon group in 2014. This thesis describes our efforts to expand their scope and utility in a variety of challenging chemical transformations.

Chapter 2 describes the development and application of immobilised bifunctional iminophosphorane organocatalysts. We have successfully immobilised bifunctional iminophosphoranes on a crosslinked polystyrene support and applied this sold-supported catalyst to three challenging asymmetric reactions; namely the nitro-Mannich reaction of phosphinoyl ketimines and the conjugate addition of alkylmalonates and N,N-dimethyl β-keto amides to nitrostyrene. Very good yields, enantio- and diasteroselectivities were obtained in all cases. We have also demonstrated their use in a range of conjugate additions of cyclic 1,3-dicarbonyl compounds to nitroalkenes, which suffered from very slow reaction rates under tertiary amine-based bifunctional catalysis. In all cases, the immobilised bifunctional iminophosphoranes performed very well in comparison to their homogeneous counterparts. We have also demonstrated catalyst recycling over 10 cycles and application in a continuous flow system with a productivity of 7.20 mmol _producth^-1g_catalyst^-1.

to the ring-opening polymerisation (ROP) of cyclic esters. We have demonstrated the performance of bifunctional iminophosphorane organocatalysts in the ROP of L-lactide (LA), δ-valerolactone (VL) and ε-caprolactone (CL). The polymerisation of LA and VL proceeded rapidly and was well controlled, while only short lengths (> 100 DP) of poly(CL) could be prepared in a controlled fashion due to hypothesised competing initiation from the catalyst. We have shown that the polymerisation of LA using our catalyst may be considered a living polymerisation. Di-block co-polymers could also be successfully prepared via sequential monomer addition or through the use of macroinitiators. We then investigated the roles of the iminophosphorane and the thiourea component of the catalyst.

Authors: Goldys, A; Anna Goldys

• Publication date: 2014
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: Oxford University, UK
• Language: English
• Keywords: bifunctional organocatalysis; solid-supported catalysts
• Subjects: Asymmetric catalysis; Organic chemistry; Synthetic organic chemistry