New organometallic strategies for conjugate addition and cross-coupling reactions

Andrews, Philip Ian (2013) New organometallic strategies for conjugate addition and cross-coupling reactions. PhD thesis, University of Nottingham.

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Abstract

Enamine N-oxides have been reported only a very few times in the literature. Investigation into their reactivity has revealed that treatment with catecholborane can generate amines via an electrophilic iminium species, which provides evidence for a proposed reverse polarity reactivity, with respect to existing 1,4-additions to nitro alkenes. Deprotonation at the α-carbon of enamine N-oxide double bonds has also been accomplished by tBuLi, with deprotonation occurring fully after 5 min. Using methodology developed within the group, a novel enamine N-oxide has been synthesised in good yield, although attempts to form a cyclic enamine N-oxide were unsuccessful.

The copper-catalysed asymmetric conjugate addition of trimethylaluminium to nitroalkenes was found to give moderate enantioselectivity (46 % ee) using Cu(OAc)2 and a phosphoramidite ligand in diethyl ether. Conjugate addition of dimethyl(alkynyl)aluminium reagents to cyclic and acyclic enones has been achieved in a racemic sense in good to excellent yields employing MTBE as the solvent with three equivalents of alkynylaluminium, although regioselectivity remains an issue depending on the enone substrate.

Cross-coupling of dimethyl(alkynyl)aluminiums with aryl bromides, iodides and triflates catalysed by Pd2(dba)3∙CHCl3 or Pd(dba)2 and DavePhos gave acetylene derivatives in good to excellent yields. These results are comparable with previously reported systems and in some cases gave improvements in yield. Using XPhos as ligand and adding DABCO, chlorobenzene was also coupled in moderate yield. Application to tetracene synthesis was not successful.

Development of a novel method of alkyne hydroalumination using dichloroalane bis(tetrahydrofuran) adduct and catalytic Ti or Zr metallocene complexes gave high yields of vinylaluminium reagents. Use of these reagents in Pd-catalysed cross-coupling with aryl halides gave good to excellent yields of (E)-alkenes, and is applicable to both aryl and alkyl terminal acetylenes.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Woodward, S.
Stockman, R. A.
Faculties/Schools: UK Campuses > Faculty of Science > School of Chemistry
Item ID: 13807
Depositing User: EP, Services
Date Deposited: 17 Nov 2015 11:05
Last Modified: 06 May 2020 15:01
URI: http://eprints.nottingham.ac.uk/id/eprint/13807

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