Ethyl 4-bromo-3-methyl-2-butenoate

Thus, condensation with ethyl 4-bromo-3-methyl-2-butenoate (2E/2Z 50/50) provided the sulphone-ester, as a mixture of isomers (13 /13Z 50/50). Elimination to the ethyl 9-methylene-retinoate (2E/2Z 50/50) was done by treating the crude mixture with EtONa in cyclohexane, Fig. (42). 

EthoxycarbonyI-2-methylalIy triphenylphosphonium bromide (1). Prepared by reaction of ethyl 4-bromo-3-methyl-2-butenoate with P sHs. 1... 

Alternatively aldehyde 4 has been prepared by Reformatsky reaction of P-cyclocitral 5 with ethyl 4-bromo-3-methyl-2-butenoate 6 (Scheme 2). DIBAL reduction of lactone 7 afforded the lactol, which was opened with HCl to afford 4 in 75% yield. The success of this reaction is dependent on the pKa of the acid, the reaction concentration and the temperature.(20)... 

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