Sulphonyl carboxylic esters

This t5rpe of reaction was originally carried out with ethyl iodide and has been extended to other alkyl halides, halogeno-carboxylic esters and to substituted arsine halides. Incidentally when j-toluene sulphonyl chloride and naphthalene-2-sulphonyl chloride were allowed to react with sodium diethyl phosphite, the corresponding disulphones were obtained in small yield. ... 

Electrolysis of isoprenoids in an aqueous sodium chloride-dichloromethane system results in a regioselective ene-type chlorination of the terminal iso-propylidene group to give allylic chlorides, e.g. (113)->(114). Acetylenic, sulphonyl, and carboxylic ester groups are not affected by the reaction conditions, but isoprenoids containing hydroxyl groups give lower yields. 

Monocyclic Selenophens.—Selenophen has been prepared from butadiene and selenium dioxide. Selenophen-3-malonic esters have been prepared by condensation of l,4-dichlorobut-3-en-2-one with malonic esters followed by reaction with sodium selenide and cyclization. 2-(2-Selenienyl)-3,4-dicarbeth-oxyfuran has been prepared analogously to the thiophen derivative.The transient absorption spectra in the flash photolysis of selenophen have been studied. "" Butyl-lithium and phenyl-lithium attack 2,5-dimethoxyselenophen at the selenium atom, giving dibutyl selenide and diphenyl selenide, respectively, together with some dienes. " Quantitative studies of the acid- and base-catalysed hydrolyses of ethyl selenophen-2-carboxylate, of the reactions of selenophen-2-sulphonyl chloride and of 2-(chloromethyI)selenophen with aniline, and of selenophen-2-carboxaldehyde with aniline and with a phosphorus ylide have been carried out. The results were rationalized by correlation analyses with polar or electrophilic constants of heterocycles, depending on the electron demand of the side-chain. ""... 

Protection of the carboxyl of Asp/Glu by 2,4-dimethoxybenzyl (Dmb) esters provides an approach for head-to-tail cyclic peptide formation (ffi). The Dmb ester can be removed selectively by 1% v/v TFA in DCM in the presence of tBu- and sulphonyl-based side-chain protection within minutes. However, the technique is limited as these conditions are sufficient to remove the side-chain trityl protection of Cys and His residues. Minor incidental loss of rBu during this procedure has also been reported (83). 

Full details of the total synthesis of ( )-pyrenophorin (107) have been published. The final cyclization was affected using di-imidazoyl-l-yl ketone as lactonizing reagent. The synthesis also features the use of the 2-(tolyl-/7-sulphonyl) ethyl protecting group for carboxylic acids selective removal of this group in the presence of other esters is easily achieved (DBN 25 °C). 

---