Dithioesters Diels-Alder reactions

Conjugation of the double bond with the thiocarbonyl was readily obtained by treatment with a catalytic amount of triethylamine for the (3-unsaturated dithioesters (4d), (4e) and (4f). At room temperature only dimers (resulting from a Diels-Alder reaction) were isolated [153] for the a-elhylenic dithioesters (4h) and (4i), derived from (4d) and (4f). 

Sulfur- and Selenium-containing Compounds. A new route to a-thioalkyl-phosphonates (292) and -phosphinates (294) has been reported from the reaction of selenothioic acid S-esters (291) with phosphites and phosphinites, respectively. By-products (293), derived from the P(III) ester alkylating the Se atom, are formed in many cases. a-Phosphono-p-substituted a,P-unsaturated dithioesters (296), prepared from diethyl phosphonodithioacetate (295), undergo Diels-Alder reactions with enol and thioenol ethers to give excellent yields of novel 5-... 

The reaction of methyl dithiocrotonate with cyclopentadiene was shown to provide the cycloadduct 13. The initial assumption that the product was derived from dithioester 2ir participation in an all-carbon Diels-Alder reaction with cyclopentadiene followed by a PPJ-sigmatro pic rearrangement was shown not to be operative. Consequently, the generation of 13 resulted from the direct 4ir participation of the a,/3-unsaturated dithioester in a Diels-Alder reaction with cyclopentadiene [Eq. (8)]. ... 

Thiocarbonyl compounds have been employed in Diels-Alder reactions to prepare thiopyranyl systems,1 and generally the carbon-sulfur double bond serves as the 2it dienophile component of the [4 + 2] cycloaddition (Chapter 5). However, there are several reported examples of a,j8-unsaturated thioaldehydes, thioketones, and dithioesters participating as the diene partners of Diels-Alder reactions in which the thiocarbonyl group comprises a component of the 4tt diene system. 

With the development of dependable approaches to the generation of a,i3-unsaturated dithioesters16-18 and with the recognition that additional alkyl substitution stabilizes the monomeric form,18 a study of their intermolecu-lar Diels-Alder reactions has been described (Scheme 8-III).18 Representative electron-deficient, strained, and electron-rich olefins participate in [4 + 2] cycloadditions with the in situ generated a,/3-unsaturated dithioesters. The HOMODiels-Alder reactions proceed preferentially through an endo [4 + 2] transition state, and the LUMOaene con-... 

P-Oxo dithioester 53 was prepared from ketone 54 on treatment with dimethyl trithiocarbonate in the presence of t-BuOK in a mixture of benzene and DMF (Scheme 13) [47]. Spectroscopic observations revealed that the dithioester 53 exists mostly in the enolic form 55. The reaction of 53/55 with hydrazine gives the tricyclic compound 56. A Diels-Alder reaction of 9-methylanthracene with 57 forms the adduct 58 in 93% yield (Scheme 14) [48]. The thermolysis of 58 in refluxing chloroform resulted in the elimination of PhSO, yielding anthracenecarbodithioate 59 with a yield of 82% through the carbocation intermediate 60. 

A review of the asymmetric thia-Diels-Alder reactions of chiral dithioesters with dienes has been published. The asymmetric organocatalytic thio-Diels-Alder reac- 0 tion of thiocarbonyls with a-methylene carbonyl dienes produced dihydrothiopyrans in high yields and high to excellent selectivities. The inverse-electron-demand 0 hetero-Diels-Alder cycloadditions of norbomene (106) with 5-benzylidene-2-arylimino-3-aryl-thiazolidine-4-thiones (107) at 25 °C produced cycloadducts (108)... 

Dithioesters bearing a chiral auxiliary have been used in asymmetric thia-Diels-Alder reactions with acyclic 1,3-dienes to produce cycloadducts with a diastereomeric excess of 90%. A Cu(II)bis(oxazoline)/dithioesters complex has been proposed to rationalize the chiral induction ... 

Certain dithioesters possessing an electron-withdrawing group will participate in the Diels-Alder [4+2] cycloaddition reaction with dienes thus, the dithioester (54b) yields the cycloadduct (66) (Scheme 37). 

Figure 12.21 Hetero-Diels-Alder (HDA) reaction between diene and electron-de cient dithioesters in the RAFT-HDA approach to make block copolymers.

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