Alkenes hydroxy conjugated esters

A more difficult problem is encountered when it is necessary to reduce selectively multiple bonds in the side chain, especially when they are conjugated with the nucleus. Up to the present time little has been published on this subject. The best method for the side chain reduction of /3-2-furylacrylic acid seems to be with Raney alloy in dilute NaOH. If the reaction is carried out more drastically, the nucleus undergoes easy reduction to give 4-hydroxy-valerolactone. The method of Railings and Smith also appears to be successful this involves the use of palladium strontium carbonate for the reduction of the alkene side chain of 2 -furylalkenes, without affecting the ring. Such compounds as j8-2 -furylacrylic esters are exceptions, but the potassium salt of the acid can be selectively reduced in aqueous solution. 

The resulting mixed aldol should be a reasonable one, since benzaldehyde has no alpha protons and the only enolate (Nu ) present would be from methyl acetate. Sodium methoxide is a good choice of base, since it would not give a new product if an addition/elimination (acyl substitution) mechanism were to take place at the ester carbonyl (i.e., no hydrolysis or transesterification will take place if the alkoxide base matches the alkoxy group of the ester). Heat is added to the reaction conditions to imply that the a,P-unsaturated product is desired, rather than the 3-hydroxy product. However, since the resulting alkene is in conjugation with both the carbonyl and the phenyl group, this dehydration is likely to occur spontaneously even at room temperature. 

Primary tosylates are more prone than bromides to form f-butyl ethers by Sn2 displacement by the f-butoxide anion in DMSO. Sulfonate esters of flexible cyclic and secondary acyclic alcohols give predominately alkenes in the presence of f-BuOK/DMSO. With sulfonate esters of 3-hydroxy steroids, there is competition between /S-elimination and attack of the f-butoxide ion on sulfur to form alcohols mesylates are more prone to this reaction than tosylates. Sulfonate esters of 3a-acetoxy-12a-hydroxycholanate undergo mainly /3-elimination with f-BuOK/DMSO (eq 4). In this case, substitution of various other aprotic solvents for DMSO and DMSO Na+ for f-BuOK was not as effective. Treatment of both the mesylate and the tosylate of cholesterol with f-BuOK/ DMSO gives the conjugated diene, 3,5-cholestadiene, in high yield. ... 

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