Known reagents that transfer three alkyl groups of a trialkylborane intramolecularly to a single carbon atom lack features to influence stereochemistry. We have investigated four reagents of type LiCCl2X, where X might be amenable to variation. All behaved differently. With X=OR (R=cyclohexyl, menthyl), the reagent decomposed, leading to only low yields of triple migration products. With X=S(O)Ph, a single migration occurred, followed by isomerisation to boron enolate-like species that hydrolysed to α-chloroalkyl phenyl sulfoxides or reacted with aldehydes to aldol-like products. With X=SO2Ph, the major product was the corresponding α,α-dichloroalkyl phenyl sulfone, apparently formed through a redox reaction. With X=S(O)(NMe)Ph, products of three intramolecular alkyl migrations were obtained with unhindered trialkylboranes. Attempts have been made to gain understanding of the sulfoxide process by investigating proportions of aldol-like products, using X-ray crystallography and ab initio calculations.

Methods for generating tert-alkyl organoboron species are in high demand as they are invaluable intermediates for the synthesis of quaternary carbon centres. Herein we report investigations into generation of tert-alkyl organoboron species using imidoyl chlorides as reagents in the organoboron cyanidation reaction. Although alkenyl side-products predominate in particularly hindered cases, tert-alkyl organoboron species can be successfully generated for less hindered examples.

The reagent 3-chloro-1-lithiopropene (4) can be generated by treating 1-bromo-3-chloropropene with t-BuLi. It is unstable but if generated at low temperature in the presence of alkylboronic esters, such as 3, is trapped in situ to give rearrangement products 2, which on oxidation give 3-alkylprop-1-en-3-ols in good yields. The reaction works for primary, secondary, benzylic, and even tertiary alkylboronic esters, providing allylic alcohols bearing almost any alkyl group available using organoborane chemistry and incorporating all features of such groups.

The reactions of bromomethyllithium with tert-alkylboronic esters could be of great potential for the formation of quaternary carbon centers but often give poor yields/conversions. Calculations and experimental evidence show that tert-alkyl groups migrate less effectively than other types of alkyl group in such reactions and that O-migration competes. Furthermore, slow/incomplete capture of the bromomethyl reagent by the boronic ester is a problem in more hindered systems, and an additional competing reaction, possibly Li–Br exchange on the bromomethylborate species, also leads to lower yields of migrated products. Based on this, experimental protocols have been devised in which the competing reactions are largely suppressed, leading to higher conversions to migrated product for several substrates.

For reactions of alkyldioxaborolanes with halomethyllithium reagents, migrations of tertiary alkyl groups and benzylic groups often give lower yields of migrated products. The only published computational study calculated the barriers to tert-alkyl migration to be lower than for other types of simple alkyl groups. In contrast to this, the present work shows that, when detailed conformational analysis is carried out, tert-alkyl and benzylic groups have significantly higher gas phase barriers to migration than for other types of alkyl groups, such that for tertiary alkyl groups, oxygen migration of the ethylenedioxy group could compete. The barriers are reduced when a solvent model is included, which reduces the importance of oxygen migration.

The deprotonation and alkylation of 1-methylcyclohexa-2,5-diene-1-carboxylic acid has been investigated under a range of conditions. In all cases, the formation of compounds 14 was found to be completely stereoselective, although compound 14c was formed as an impurity when alkyl iodides were used as electrophiles, and doubly-alkylated compounds 17 were formed in some cases when alkyl bromides were used.

Alkylidenepyrrolidines 1, 21, 24 and 26 undergo reactions with nitrile oxides and nitrilimines or their precursors to give a range of novel heterocyclic compounds. With alkylidenepyrrolidine ester 1, nitrolic acids give products in which the liberated nitrous acid reacts with the alkylidenepyrrolidine, followed by two cycloadditions to give adducts 3. In contrast, hydroximoyl chlorides give isoxazoles 10, presumably by cycloaddition/elimination. With hydrazonyl chlorides, simple acylation of the alkylidenepyrrolidine occurs to give compounds 17. With sulfonyl alkylidenepyrrolidines 24 and 26, cycloaddition onto the imine tautomer is the preferred pathway, with a stereoselective reaction taking place in the latter case.

Lycoposerramine A (1) is a pentacyclic alkaloid isolated in 2001 by Takayama and co-workers. A concise synthesis of a model compound 8 for the tetracyclic core of this natural product is described. Key steps include the desymmetrising free-radical cyclisation of compound 7 to give compound 18 and spirocyclisation of compound 26 to give compound 8. Earlier approaches using a novel high-yielding stereoselective anionic cyclisation of a cyclohexa-1,4-diene are also reported.

Batzelladine C (3) is a tricyclic guanidine alkaloid of unknown stereochemistry at one centre as well as unknown absolute stereochemistry. The two possible diastereoisomers of the methyl ester corresponding to this compound have been synthesised, permitting the relative and absolute stereochemistry of this compound to be assigned.

Epoxidation/cyclisation of cyclohexa-1,4-dienes containing pendant hydroxyl groups provides stereocontrolled access to highly-functionalised reduced benzol[b]furan derivatives.

The tricyclic core of lycoposerramine S has been synthesised in 10 steps from a symmetrical cyclohexadiene precursor by way of a desymmetrising free-radical cyclisation and iodocyclisation.

Application of a diastereoselective three-component coupling to the bicyclic core of the batzelladine alkaloids is described. The synthesis features the elaboration of glutamic acid by use of Eschenmoser sulfide contraction. An earlier approach is also included, which shows some limitations of dithiane chemistry when applied to the particular compounds required for this target.

An improved synthesis of the 1,1′,2,2′,3,3′,4,4′-octahydro-1,1′-biisoquinoline ring system is described. The reactivity of this system has been investigated, including the unusually high basicity of the parent compound and its N,N′-dimethyl derivative. The resolution of the parent compound has been achieved for the first time, along with the development of a straightforward method for assaying its enantiomeric purity.

A new chiral proton sponge has been prepared, and the reasons for its unusually high basicity elucidated by a quantum chemical study.

The tricyclic core of lycoposerramine S has been synthesised in 10 steps from a symmetrical cyclohexadiene precursor by way of a desymmetrising free-radical cyclisation and iodocyclisation.

Epoxidation/cyclisation of cyclohexa-1,4-dienes containing pendant hydroxyl groups provides stereocontrolled access to highly-functionalised reduced benzol[b]furan derivatives.

Lycoposerramine A (1) is a pentacyclic alkaloid isolated in 2001 by Takayama and co-workers. A concise synthesis of a model compound 8 for the tetracyclic core of this natural product is described. Key steps include the desymmetrising free-radical cyclisation of compound 7 to give compound 18 and spirocyclisation of compound 26 to give compound 8. Earlier approaches using a novel high-yielding stereoselective anionic cyclisation of a cyclohexa-1,4-diene are also reported.

Alkylidenepyrrolidines 1, 21, 24 and 26 undergo reactions with nitrile oxides and nitrilimines or their precursors to give a range of novel heterocyclic compounds. With alkylidenepyrrolidine ester 1, nitrolic acids give products in which the liberated nitrous acid reacts with the alkylidenepyrrolidine, followed by two cycloadditions to give adducts 3. In contrast, hydroximoyl chlorides give isoxazoles 10, presumably by cycloaddition/elimination. With hydrazonyl chlorides, simple acylation of the alkylidenepyrrolidine occurs to give compounds 17. With sulfonyl alkylidenepyrrolidines 24 and 26, cycloaddition onto the imine tautomer is the preferred pathway, with a stereoselective reaction taking place in the latter case.

The deprotonation and alkylation of 1-methylcyclohexa-2,5-diene-1-carboxylic acid has been investigated under a range of conditions. In all cases, the formation of compounds 14 was found to be completely stereoselective, although compound 14c was formed as an impurity when alkyl iodides were used as electrophiles, and doubly-alkylated compounds 17 were formed in some cases when alkyl bromides were used.

Batzelladine C (3) is a tricyclic guanidine alkaloid of unknown stereochemistry at one centre as well as unknown absolute stereochemistry. The two possible diastereoisomers of the methyl ester corresponding to this compound have been synthesised, permitting the relative and absolute stereochemistry of this compound to be assigned.