Thiobenzoates, rearrangement

A reaction similar to the Claisen reaction is the [3,3]sigmatropic rearrangement of an allyl thiobenzoate into an allyl thiolbenzoate, as shown in Eq. (5-51) [156]. 

In a similar way, the reaction of xanthates under radical conditions leads to products and selectivities that are totally different from those in thermal rearrangements. The radical transformation usually furnishes unsubstituted hydrocarbons as reaction products. The major accomplishment of the reaction is the deoxygenation of secondary alcohols to furnish the corresponding hydrocarbons when tributylstannane is used with 0-cycloalkyl thiobenzoates or S-methyl dithiocarbamates [13]. However, the rearranged product may be observed as a byproduct [14,15]. 

The rate of the rearrangement of allyl, crotyl and a-methylallyl thiobenzoates in a variety of solvents is conveniently followed by spectroscopic methods. The comparative lack of sensitivity of the first-order rate coefficients to solvent ionizing power was attributed to the small difference in charge separation between ground state and transition state. 

Dehydration of homoallylic alcohols. 0-Cholesteryl thiobenzoate (1, X ,ax 256, 288, and 420 nm) on irradiation in cyclohexane with a medium-pressure mercury vapor lamp for 12 min. is converted into 3,5-cholestadiene (2) and thio-benzoic acid in quantitative yield. Similar irradiation of O-cholestanyl thiobenzoate results merely in rearrangement to the thiobenzoic acid S-ester hence the elimination reaction appears to require some conjugation in the transition state of the newly formed bond. ... 

Hydrolysis of the trifluoroacetyl-derivative (153) produces a mixture of the pyrrolin-2-ones (154) and (155) the latter is unstable, and gradually isomerizes to the former." Whereas the 7V-benzyl- and N-phenyl-pyrrolin-3-ones (156 R = CH2Ph or Ph) exist in the keto form shown, the iV-methyl derivative forms an equilibrium mixture of keto (156 R = Me) and enol tautomers (157)." The reaction of the pyrrolinone (158) with p-nitrobenzaldehyde unexpectedly yields compound (159)." The product of the action of thiobenzoic acid on (160) is the spiro-pyrrolinone (161), contrary to a previous report." Treatment of p-hydroxyphenylacetic acid with di-isopropylcarbodi-imide gives the imino-pyrrolinone (162), which rearranges to the bridged spiro-compound (163) in the presence of boron trifluoride etherate." ... 

The rearrangement of alkyl thiobenzoates had also been reported in certain cases. An application of this reaction is the thermal conversion of thionesters of glycerol to esters of thioglycerol (85->8Q . 

A Study of the rearrangement of the optically active exo-norbomyl thiobenzoate 89 to 90 showed that the rate of racemization was equal to the rate of the disappearance of 89. This indicates that no return via the oxygen occurs . ... 

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