Cycloaddition Reactions of Thioxoacetate Esters With Unsymmetrical Dienes

The Diels-Alder reaction of transient thioxoacetate esters, RO2C. CHS, generated under mild, basic conditions from the Bunte salts, RO2C.CH2SSO3Na, has been studied with a variety of unsymmetrical, conjugated dienes. Specifically, ethyl thioxoacetate was generated from the Bunte salt, EtO2C.CH2SSO3Na, and trapped with 1-methoxy-1,3-cyclohexadiene, ethyl 3,5-hexadienoate, and the dienamine derived from Pummerer's ketone. Methyl 2,4-hexadienoate did not act as an effective trapping agent under these conditions. The regiochemistry, stereochemistry, and relative yields of the cycloadducts from each unsymmetrical diene are discussed. The retro-Diels-Alder reaction has also provided a good method for the generation of thioxoacetate esters. Ethyl thioxoacetate was generated by thermal cleavage of the corresponding anthracene cycloadduct, and was trapped in situ with 1-methoxy-1,3-cyclohexadiene. Similarly, the cycloadduct of methyl 2,4-hexadienoate and methyl thioxoacetate was obtained in good yield using the corresponding anthracene adduct as a source of the thioaldehyde. An intramolecular Diels-Alder reaction has been carried out successfully. The anthracene adduct of 3,5-hexadien-1-yl thioxoacetate was prepared by esterification of the corresponding acid. This cycloadduct dissociated in toluene at 11

Cycloaddition Reaction of Ethyl Thioxoacetate and the Dienamine Derived from Pummerer's Ketone

The objective of this work is to study the regio- and stereochemistry of the cycloadducts obtained from the treatment of ethyl thioxoacetate and the dienamine derived from Pummerer's ketone