Disodium prephenate

Vinyl sulfoxides are useful Diels-Alder dienophiles. Thermolysis of the adducts gives rise to alkenes via sulfoxide elimination and so over the two steps the vinyl sulfoxides are the synthetic equivalents of alkynes, e.g. phenyl vinyl sulfoxide reacts with anthracene and 1,4-diphenylbuta-1,3-diene with concomitant sulfoxide elimination under the Diels-Alder conditions to give adducts (70) and (71 Scheme 15). 3-Phenylsulfinyl-a,3-unsaturated-carbonyl compounds have also been used as Diels-Alder dienophiles in chemistry developed for a synthesis of disodium prephenate and epiprephenate. With the electron rich diene (72), vinyl sulfoxides (73) and (75) gave rise to products (74 equation 33) and (76 equation 34) after hydrolysis. For the prephenate synthesis the phenylsulfinylmethylenelactone (77) was used, giving cyclohexadienone (78 Scheme 16) after sulfoxide elimination and hydrolysis. ... 

Cycloaddition of the diene 20 with dienophiles bearing a phenyl sulfoxide substituent leads, after elimination of phenyl sulfenic acid and hydrolysis, to a 4,4-disubstituted cyclohexadienone or a substituted phenol product. For example, an elegant synthesis of disodium prephenate 34 makes use of this chemistry... 

Disodium Prephenate.—Biosynthetic pathways seem to be characterized by the occasional presence of elusive chemical substances, elusive by virtue of their transient nature as free chemical entities. One such is prephenic acid (12), an... 

DANISHEFSKY, S., M. HIRAMA, N. FRITSCH, J. CLARDY. 1979. Synthesis of disodium prephenate and disodium epiprephenate. Stereochemistry of prephenic acid and an observation on the base-catalyzed rearrangements of prephenic acid to p-hydroxyphenyllactic acid. J. Am. Chem. Soc. 101 7013-7018. 

Full reports have appeared on total synthesis of disodium prephenate (18) (2, 40). 

This new route to cyclohexadienones has been used in a total synthesis of the disodium salt of prephenic acid (2j, an unstable intermediate in biosynthesis of various phenols. The first attempt used the dienophile 3 in which the potential... 

Danishefsky and Hirama have published a neat total synthesis of the disodium salt of prephenic acid (24), a central intermediate in the shikimic acid biosynthetic pathway.The key step involves a Diels-Alder reaction between the diene (22) and the unsaturated lactone (23). A crucial feature of this synthesis is the simultaneous protection of both the C-lO-carboxy and C-8-keto functions as a methoxy-lactone, allowing umasking in a single step by alkaline hydrolysis. 

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