Alison J. Redgrave

ASYMMETRIC CATALYSIS OF ACYL TRANSFER BY LEWIS ACIDS AND NUCLEOPHILES. A REVIEW

INTRODUCTION .............................................................................................................................. 333 I. CHIRAL LEWIS ACID CATALYSIS ........................................................................................ 334 11. CHIRAL NUCLEOPHILE CATALYSIS ................................................................................. 338 CONCLUSIONS ................................................................................................................................ 3.56 REFERENCES ................................................................................................................................... 3.57

Stereoselective 1,2‐cis Glycosylation of 2‐O‐Allyl Protected Thioglycosides

The technique of intramolecular aglycon delivery (IAD), whereby a glycosyl acceptor is temporarily appended to a hydroxyl group of a glycosyl donor is an attractive method that can allow the synthesis of 1,2-cis glycosides in an entirely stereoselective fashion. 2-O-Allyl protected thioglycoside donors are excellent substrates for IAD, and may be glycosylated stereoselectively through a three-step reaction sequence. This sequence consists of quantitative yielding allyl bond isomerisation, to produce vinyl ethers that can then undergo N-iodosuccinimide mediated tethering of the desired glycosyl acceptor, and subsequent intramolecular glycosylation, to yield either alpha-glucosides or beta-mannosides accordingly. Although attempted one-pot tethering and glycosylation is hampered by competitive intermolecular reaction with excess glycosyl acceptor, this problem can be simply overcome by the use of excess glycosyl donor. Allyl mediated IAD is a widely applicable practical alternative to other IAD approaches for the synthesis of beta-mannosides, that is equally applicable for alpha-gluco linkages. It is advantageous in terms of both simplicity of application and yield, and in addition has no requirement for cyclic 4,6-protection of the glycosyl donor.

Catalytic enantioselective intermolecular cycloadditions of a 2-diazo-3,6-diketoester-derived carbonyl ylide with alkyne and strained alkene dipolarophiles

Catalytic enantioselective tandem carbonyl ylide formation-cycloaddition reactions of tert-butyl 2-diazo-3,6-dioxoheptanoate 7 with alkyne and strained alkene dipolarophiles to afford the corresponding cycloadducts with up to 92% ee are described.

[3+2] Cycloaddition reactions of arylacetylenes with carbonyl ylides derived from 1-aryl-1-diazohexane-2,5-diones

The synthesis and 1,3-dipolar cycloaddition reactions of α-aryl-α-diazodiones with aryl acetylenes (up to 76% ee) are described.

Synthesis of unprotected and borane-protected cyclic phosphines using Ru? and Mo? based olefin metathesis catalystsThis is one of a number of contributions from the current members of the Dyson Perrins Laboratory to mark the end of almost 90 years of organic chemistry research in that building, as all its current academic staff move across South Parks Road to a new purpose-built laboratory.

Ru- and Mo-based catalysts can be used in ring closing metathesis (RCM) reactions to synthesise cyclic phosphines protected as their borane complexes. The compatibility of the Schrock Mo-catalyst and the N-heterocyclic carbene Ru-catalysts with this class of substrates is particularly noteworthy as asymmetric RCM (ARCM) is now emerging as a new tool for the preparation of homochiral phosphines. One of the key results is that the Mo-catalyst allows the ring closure of the unprotected diallylphenylphosphine with 95% conversion.

Atropisomeric α-methyl substituted analogues of 4-(dimethylamino)pyridine: synthesis and evaluation as acyl transfer catalysts

The regioselectivity of α-metalation–methylation of N-BF3 adducts of 4-(dimethylamino)pyridines as a function of β-substitution is examined in attempts to prepare configurationally stable atropisomeric derivatives (I and II) having an α-methyl substituent and a β-biaryl stereogenic axis. The activity of some of these derivatives as catalysts for acyl transfer is examined and the kinetic resolution of 1-(1-naphthyl)ethanol catalysed by α-methyl chiral DMAP (−)-24 is reported. A rationale for the reduced stereoselectivity of this catalyst relative to its non-α-substituted analogue (−)-1 is also proposed.

Synthesis of C2-symmetric analogues of 4-(pyrrolidino)pyridine: new chiral nucleophilic catalysts

The syntheses of a series of enantiomerically pure C2-symmetric 4-(pyrrolidino)pyridine (PPY) derivatives by SNAr of 4-halo-/4-phenoxypyridines and by cyclocondensation from 4-aminopyridine are described. Preliminary results pertaining to their use as catalysts for acylative kinetic resolution of 1-phenylethanol are also presented. A single-crystal X-ray analysis of PPY If is reported.

Stereoselective cis glycosylation of 2-O-allyl protected glycosyl donors by intramolecular aglycon delivery (IAD)

2-O-Allyl protected glycosyl donors may be glycosylated stereoselectively via a three step sequence involving double bond isomerization, N-iodosuccinimide mediated tethering to a glycosyl acceptor and subsequent intramolecular glycosylation (intramolecular aglycon delivery, IAD).

Allyl Protecting Group Mediated Intramolecular Aglycon Delivery (IAD) of Glycosyl Fluorides

Stereospecific 1,2-cis-glycosylation of 2-O-allyl protected glucosyl and mannosyl fluorides can be achieved via a sequence of allyl isomerization, N-iodosuccinimide mediated tethering, and intramolecular aglycon delivery (IAD). Fluoride is advantageous as an anomeric leaving group since extended reaction times can be employed to tether hindered aglycon alcohols without competitive anomeric activation. Tin(II) chloride mediated intramolecular glycosylation furnishes the desired α-glucosides and β-mannosides in an entirely stereoselective manner.