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.

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 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.

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.

Highly regioselective di-tert-amylation of naphthalene using different alcohols can be achieved over a H-mordenite (HM) zeolite. For example, the tert-amylation of naphthalene using tert-amyl alcohol in cyclohexane over HM (Si/Al = 10) zeolite has been optimised to give a 70% yield of 2,6-dialkylnaphthalenes, of which 2,6-di-tert-amylnaphthalene was produced in 46% yield along with 2-tert-amyl-6-tert-butylnaphthalene (23%) and 2,6-di-tert-butylnaphthalene (1%). This has been achieved by varying the reaction time, temperature, pressure and amounts of tert-amyl alcohol and zeolite. No 2,7-dialkylnaphthalenes were seen under the conditions tried. The zeolites can be easily regenerated by heating and then reused.

Unexpectedly, lithiation of N′-(2-(2-methylphenyl)ethyl)-N,N-dimethylurea with 3 equiv of n-butyllithium in anhydrous THF at 0 °C takes place on the nitrogen and on the CH2 next to the 2-methylphenyl ring (α-lithiation). The lithium reagent thus obtained reacts with various electrophiles to give the corresponding substituted derivatives in excellent yields. Similarly, lithiation of N-(2-(2-methylphenyl)ethyl)pivalamide under similar reaction conditions followed by reaction with benzophenone as a representative electrophile gave the corresponding α-substituted product in high yield. Surprisingly, no products resulting from lateral lithiation were observed under the conditions tried, which sharply contrasts with the reported results for lateral lithiation of tert-butyl (2-(2-methylphenyl)ethyl)carbamate.

Electrophilic aromatic substitution is one of the most important reactions in synthetic organic chemistry. Such reactions are used for the synthesis of important intermediates that can be used as precursors for the production of pharmaceutical, agrochemical and industrial products. However, many commercial processes to produce such materials still rely on technology that was developed many years ago. Such processes commonly lead to mixtures of regioisomers and in recent years several new approaches have been developed to gain control over the regiochemistry of the reactions. Zeolites can act as heterogeneous catalysts, support reagents, entrain by-products, enhance product para-selectivities via shape-selectivity and avoid aqueous work-ups. For example, zeolites can have advantages in para-regioselective nitration, halogenation, alkylation, acylation and methanesulfonylation reactions under modest conditions. Moreover, usually they can be easily removed from reaction mixtures by simple filtration and regenerated by heating and can then be reused several times to give almost the same yield and selectivity as fresh samples. This review surveys the use of zeolites as para-selective catalysts for a whole range of aromatic substitution reactions, based largely on our own work in the area, but set in the wider context of other related work.

Lithiation of various N′-benzyl-N,N-dimethylureas with t-BuLi (3.3 mole equivalents) in anhydrous THF at 0 °C followed by reactions with various electrophiles afforded the corresponding 3-substituted isoindolin-1-ones in high yields.

Nitration of benzonitrile was investigated using a nitric acid/acid anhydride/zeolite catalyst system under different reaction conditions. Trifluoroacetic and chloroacetic anhydrides were found to be the most active among the anhydrides tried. Also, zeolites Hβ and Fe3+β (Si/Al = 12.5) were found to be the most active catalysts. For example, nitration of benzonitrile with trifluoroacetyl nitrate under reflux conditions in dichloromethane gave 3- and 4-nitrobenzonitriles in quantitative yield, of which the para-isomer represented 24–28%. The yield of para-isomer was improved to 33% when passivated Hβ was used under similar reaction conditions. This is easily the most para-selective nitration of benzonitrile ever recorded. Also, no ortho-isomer was formed under the conditions tried. The zeolite can be easily recovered, regenerated by heating and reused up to six times to give results similar to those obtained with a fresh sample of the catalyst. The nitration system was applied successfully to a range of deactivated mono-substituted benzenes to give para-isomers in significantly higher proportions than in the corresponding traditional nitration reactions.

Five new chemiluminescent aryl acridiniumcarboxylate esters 6–10, with a linker group in an ortho- or meta-position of the phenoxy ring, have been synthesized. The ortho- derivatives 6, 7 and 9 show significant improvement in the quantum yield of chemiluminescence and slower chemiluminescence kinetics compared to the unsubstituted para- derivative, 1, while the ortho- derivative 8 shows quicker chemiluminescence kinetics and a lower quantum yield of chemiluminescence. The meta- derivative 10 shows similar chemiluminescent properties to that of its para-substituted analogue.

Mononitration of phenol was investigated using iso-propyl nitrate as a nitrating agent over various zeolite catalysts under different reaction conditions. Zeolite Hβ with a low Si/Al ratio (12.5) was found to be an active catalyst for nitration of phenol under reflux conditions in dichloroethane, producing 2- and 4-nitrophenols in a ratio of around 1:1. However, zeolites H-mordenite, HY and Hβ (with high Si/Al ratio—150 or 300) gave 2-nitrophenol as the major product (ortho/para ratio = ca. 2–3).

A nitration system comprising nitric acid, propanoic anhydride, and zeolite Hβ has been developed for dinitration of toluene to give 2,4-dinitrotoluene in 98% yield, with a 2,4-:2,6-dinitrotoluene ratio of over 120. This represents the most selective quantitative method for 2,4-dinitration of toluene; the catalyst is reusable, solvent is not needed, and an aqueous work-up is not required.Graphical abstractDouble nitration of toluene with nitric acid and propanoic anhydride over zeolite Hβ gave 2,4-dinitrotoluene in 98% yield and the ratio of 2,4-:2,6-dinitrotoluenes was 123:1. This is the most selective double nitration of toluene ever recorded. The zeolite could be reused several times, which should improve the economics.Download high-res image (77KB)Download full-size imageHighlights► Nitration of toluene gave 2,4-DNT in 98%. ► Highly selective process. ► Zeolite reused.

Lithiation of various N′-benzyl-N,N-dimethylureas with t-BuLi (3.3 mole equivalents) in anhydrous THF at 0 °C followed by reactions with various electrophiles afforded the corresponding 3-substituted isoindolin-1-ones in high yields.