Allenes ethylene derivs., synthesi

Allenes from ethylene derivatives Synthesis with insertion of 1 G-atom One-step procedure... 

BoranelmethyllithiumIacetic acid Synthesis of terminal allenes from ethylene derivs. 

Ethylene and styrene derivatives react with various propargylic silyl ethers in the presence of zirconocene(II) to afford allenic products in high yield (Scheme 5.7). For example, substrate 67 was transformed into the trisubstituted allene hydrocarbon 68 in 93% yield under the reaction conditions [20]. In the synthesis of various tetraalkylated allenes, in which several of the alkyl substituents also contained triple bonds, allowing these substrates to be cydized intramolecularly into aromatic com-... 

Regioselective stannylcupration of terminal alkynes and allenes, followed by quenching of the cuprate intermediate with ethylene oxide, provides a facile synthesis of cyclobutene and alkylidine cyclobutane derivatives, respectively (Scheme 3.23) [15c]. A number of total syntheses have exploited regioselective stannylcup-... 

A general route to 6-substituted valerolactones (112) is by condensation between aldehydes and the dianion derived from butynoic acid followed by hydrogenation using Lindlar s catalyst.During the synthesis of some steroid derivatives, use has been made of an intramolecular Wadsworth-Emmonds procedure to construct an unsaturated valerolactone group (114) from phos-phonate (113) (c/. 3, 87). A new preparation of ( )-pestalotin (115) has as its pivotal step a Lewis acid-catalysed condensation between 2-benzyloxyhexanol and diketen. /3-Ethylenic valerolactones (116) can be obtained from the corresponding /3-allenic acids by treatment with methanolic boron trifluoride (c/. 3, 89). 

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