(c)17.13(b)Here we see an example of the Wittig reaction applied to diene synthesis by use of an ylidecontaining a carbon–carbon double bond.(c)Methylene transfer from methylenetriphenylphosphorane is one of the most commonly usedWittig reactions.17.14A second resonance structure can be written for a phosphorus ylide with a double bond betweenphosphorus and carbon. As a third-row element, phosphorus can have more than 8 electrons in itsvalence shell.17.15(b)Two Wittig reaction routes lead to 1-pentene. One is represented retrosynthetically by thedisconnectionThe other route is1-PenteneCH3CH2CH2CHCH21FormaldehydeOHCHButylidenetriphenylphosphoraneCH3CH2CH2CH12P(C6H5)311-PenteneCH3CH2CH2CHCH2CH3CH2CH2CHOButanalMethylenetriphenyl-phosphorane12CH
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