R. Alan Aitken

Catalytic asymmetric ring-opening of bridged tricyclic anhydrides

Abstract Cinchona alkaloid catalysed methanolysis of three different achiral tricyclic anhydrides provides convenient access to either enantiomer of the corresponding half-esters in 35–67% enantiomeric excess; the absolute configuration of the products has been determined and a convenient procedure developed for preparation of multigram quantities of either enantiomer of one half-ester in ∼90% e.e.

Thermal rearrangement of indolyl oxime esters to pyridoindoles.

Acyl oximes derived from a variety of indolylalkanones underwent a ring closure sequence during FVP to afford 9H-pyrido[2,3-b]indoles. Unlike UV light promoted reactions of oxime esters, the mechanism is almost certainly not mediated by iminyl radicals but probably involves tautomerism, elimination of acetic acid, and a final electrocyclic ring closure.

Formation of novel 1:2 adducts between bun3P.CS2 and electron-deficient alkynes

Abstract The zwitterionic adduct between tri-n-butylphosphine and carbon disulphide reacts under neutral conditions with two equivalents of dimethyl- and diethyl acetylenedicarboxylate, dibenzoylacetylene and methyl benzoylpropiolate to give novel crystalline dithiole-containing phosphorus ylides. An X-ray structure, spectroscopic and chemical properties all show these to be significantly stabilised by delocalisation.

Catalytic asymmetric synthesis of highly functionalised compounds with six contiguous stereocentres

Alcoholysis of the achiral epoxyanhydride (1) in the presence of a catalytic quantity of a cinchona alkaloid gives, in a single step, the chiral products (2) in up to 99% enantiomeric excess.

UNUSUALLY DIRECT SYNTHESIS OF MONO- AND DI-SUBSTITUTED TETRATHIAFULVALENES

Abstract Direct reaction of norbornadiene, tributylphosphine, carbon disulfide and acetylenic diesters affords the norbornene-fused dihydrotetrathiafulvalenes 7 in addition to the bis-adducts 4 and for less reactive acetylenic dipolarophiles only 7 is isolated. Upon flash vacuum pyrolysis the compounds 7 undergo a retro Diels-Alder reaction to give substituted tetrathiafulvalenes 8 . By using the norbornadiene diester in place of norbornadiene with DMAD, 8a can be obtained in higher overall yield. Attempted isolation of the zwitterionic structure 9 instead gave a rearrangement product with the novel 1,2,5-trithiepane stabilised ylide structure 11 .

Direct one pot construction of norbornane-fused dihydrotetrathiafulvalenes

Abstract Polycyclic dihydro-TTF structures can be constructed in a two-step one-pot procedure using cycloaddition of tributylphosphine/carbon disulfide adduct.

Cycloaddition of Bu3P·CS2: Formation of extended bis- and tris-1,3-dithiolanes and dithiolane-containing polymers

Abstract Reaction of the tri-n-butylphosphine/carbon disulfide adduct 1 with norbornene and aromatic di- and trialdehydes gives the bis- and tris-dithiolanes 7–9 resulting from Wittig reaction of 2. In the same reaction, norbornadiene diester 10 reacts only on the unsubstituted double bond to give bis-dithiolanes 11 and 12, while norbornadiene itself reacts on both double bonds to give novel dithiolane-containing polymers 13–15. In the bis-dithiolane 16 derived from reaction of 1, norbornene and phthalaldehyde, the groups interact leading to cyclisation so that only the spiroindane isomer 17 is obtained and its X-ray crystal structure is presented. In the reaction of 1, 10 and phthalaldehyde the initial product 21 can be observed but it similarly cyclises upon acid catalysis to afford 22. By treatment of 21 with HBF4 followed by Et3N the opposite stereoisomer 23 is mainly obtained in addition to 22.

CYCLOADDITION OF BUN3P.CS2 : DIRECT ONE-POT CONVERSION OF STRAINED DOUBLE BONDS TO 2-ALKYLIDENE-1,3-DITHIOLANES

Abstract Reaction of the adduct between tri-n-butylphosphine and carbon disulfide 1 with norbornene gives the novel zwitterionic structure 9. In solution this dissociates to the ylide 8 which undergoes Wittig reaction with aldehydes. Using the same method, the overall conversion of the strained double bond in a variety of bicyclo[2.2.1]alkenes into 2-benzylidene-1,3-dithioles 15–24 has been achieved and the reaction is also applicable to norbornadiene, affording bis-dithiolanes 29–31.

Flash vacuum pyrolysis of stabilised phosphorus ylides. Part 5. Selective extrusion of PH3PO from β,γ,β′-trioxo ylides to give diacylalkynes

Sixteen examples of the previously unknown trioxo ylides 7 have been prepared by acylation of stabilised phosphorus ylides 8 with α-oxo acid chlorides 9. Extrusion of Ph3PO from these is readily achieved using FVP at 500 °C in most cases, to afford the diacylalkynes 10 in moderate yield. Three examples failed to give the expected alkynes and the nature of the processes involved in these cases is uncertain. Fully assigned 13C NMR spectra are presented for the ylides and an unexpected pattern is observed in the value of JP–C for the three carbonyl carbons depending on the nature of the substituents present. There is some correlation between the value of 2JP–C for the central carbonyl carbon and the success of the pyrolysis although this is not complete. The method has been used to prepare a specifically 13C labelled acetylenic diester 14.

Chemical repercussions of orbital interactions through bond and through space. Effect of remote substituents on the addition of nitrenes to bicyclic olefins

Abstract The reactivity of a series of bicyclic olefins with nitrenes is profoundly influenced by the nature of remote functional groups. There is a marked lack of reactivity for reactions with carboethoxynitrene as compared to phthalimidonitrene which is distinctly nucleophilic in character. An explanation for the reluctance to form aziridines is offered in terms of orbital interactions between the distant groups and the olefinic bond, making the latter remarkably electron deficient as evidenced by UV-photoelectron spectrosoopy. Because of the complexity of the spectra, identification of the Ip associated with the reactive π-centre was made by recourse to ab initio configuration interaction calculations for key members of the series.