Allenes, with alcohols isocyanate

The 1,2-functionalization of the allene moiety in 2-azetidinone-tethered alleny-nol derivatives has also been explored [96]. Carbamate 174 was selected as the starting material for the palladium(II)-catalyzed reaction. The above carbamate was prepared from the ot-allenic alcohol 171a by treatment with tosyl isocyanate. Reaction of compound 174 was carried out at room temperature in acetonitrile in the presence of 10 mol% of Pd(OAc)2, 5 equiv of LiBr, 2 equiv of Cu(OAc)2 and 1.2 equiv of K2CO3 under an atmospheric pressure of oxygen. The 1H-XMR spectrum of the crude material displayed neither signal corresponding to the allene... 

Simple chiral allenes have been prepared by the reaction of propargylic carbamates with lithium dialkylcuprates. The diastereomeric carbamates, derived from racemic propargylic alcohols and (/ )-1-(l-naphthyl)ethyl isocyanate, are readily separated by h.p.l.c. they are then treated with lithium dialkycuprates at -78 °C, producing the allenes with enantiomeric excess up to 80% in yields of around 70% (Scheme 2). The method is claimed to be an improvement on earlier methods in that it is much simpler and gives better optical yields. 

Review. New synthetic reactions based on the onium salts of aza-arenes have been reviewed (75 references). The reactions discussed involve activation of carboxylic acids or alcohols with 2-haIopyridinium, benzoxazolium, benzothiazolium, and pyridinium salts to afford 2-acyloxy or 2-alkoxy intermediates, which can be transformed into esters, amides, thiol esters, (macrocyclic) lactones, acid fluorides, olefins, allenes, carbodiimides, isocyanates, isothiocyanates, and nitriles under appropriate conditions. 

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