The palladium-catalyzed heteroannulation of o-iodoanilines with dienyl sulfones provides a convenient route to vinylogous 2-sulfonylindolines 3. The reaction proceeds in DMF/water in the presence of potassium carbonate and catalytic palladium(II) acetate and is compatible with both electron-donating and -withdrawing substituents in the para position of the aniline, and with an alkyl substituent at C-2 of the dienyl sulfone. The indolines underwent oxidation with DDQ to afford the corresponding indoles 4. The latter were then employed as dienes in Diels-Alder reactions with dimethyl acetylenedicarboxylate (DMAD), methyl propiolate, or methyl acrylate. In the case of the latter two dienophiles, the cycloadditions were highly regioselective, affording the corresponding 1,3-products (with respect to the relative positions of the sulfone and ester groups), exclusively. The cycloadducts from acetylenic dienophiles were converted to the corresponding carbazoles by elimination of the sulfone moiety with DBU, and that from methyl acrylate was subjected to reductive desulfonylation and oxidation to the corresponding carbazole with DDQ. The method thus provides access to carbazoles with various substituents at the 3-, 4-, and 6-positions.

1-Phenylseleno-2-(p-toluenesulfonyl)ethyne (4) was produced nearly quantitatively from p-(toluenesulfonyl)ethyne and benzeneselenenyl chloride. It underwent stereo-and regioselective synadditions of organocopper reagents RCu(CN)Li to the -position of the sulfone moiety to afford adducts 5. Further reaction of the products with reagents RCu(SePh)Li resulted in substitution of the phenylseleno group with retention of configuration. Control of E,Z-stereochemistry in the product , -disubstituted vinyl sulfones is therefore achieved by the order of addition of the reagents. Selenoxide syn-elimination of adducts 5 afforded the corresponding allenic sulfones. The additions of amines and alkoxides to 4 produced the corresponding anti-Michael regioisomers (where attack occurred R to the sulfone group) as the major or sole products. The additions were highly stereoselective, proceeding by anti-addition in the anti-Michael series and by syn-addition in the corresponding Michael regioisomers. The reactions of 4 with thiolates and selenolates were more complex, affording rearranged adducts and Michael adducts as the major and minor products, respectively. The formation of the rearranged products can be rationalized by a series of additionelimination processes. Phenylselenoethyne (43) underwent conjugate additions of pyrrolidine, sodium methoxide, sodium ethanethiolate, and benzeneselenolate anion, affording the corresponding cis isomers via anti-addition. The experiments with heteroatom nucleophiles and acetylenes 4 and 43 show that the phenylseleno group has a surprisingly large activating effect upon conjugate additions.Unsaturated sulfones have numerous uses in organic synthesis. 1 The sulfone group, like the carbonyl group, has an activating effect upon an adjacent carbon-carbon double or triple bond with respect to conjugate additions and cycloadditions. The resulting products are saturated or vinyl sulfones that can be further elaborated via reactions of the corresponding sulfone-stabilized R-carbanions with electrophiles. Furthermore, subsequent reductive desulfonylation permits the sulfone moiety to act as a temporary activating group. Thus, for example, acetylenic sulfones function as the synthetic equivalents of dipoles and "multipoles", such as 1 and 2 in Scheme 1.In principle, further opportunities for synthetic transformations that can be used in conjunction with the above become possible if an appropriate nucleofuge is installed at the -position of an acetylenic sulfone. This provides the site for the introduction of an additional nucleophile by substitution of the nucleofuge (Scheme 1) or for the regeneration of unsaturation by its elimination. It appeared to us that the phenylseleno group might be an appropriate -substituent for this purpose, since certain -selenovinyl sulfones are known to undergo substitution reactions of the selenium moiety with organocuprates 2 and other nucleophiles, 3,4 as well as syn-elimination reactions of their corresponding selenoxides. 5,6 We now report the preparation of the novel...

1-Phenylseleno-2-(p-toluenesulfonyl)ethyne (1) is an effective dienophile and dipolarophile. It underwent facile Diels−Alder reactions with a variety of dienes to afford vicinal sulfone- and selenide-functionalized 1,4-cyclohexadienes. Unexpected regiochemistry that is the opposite of what is obtained with simple acetylenic sulfones was observed with several unsymmetrical dienes containing methyl or methoxy substituents at the 1- or 2-position. Acetylene 1 reacted with (trimethylsilyl)methyl azide, diazomethane, and 2,4,6-trimethylbenzonitrile N-oxide via 1,3-dipolar cycloadditions to afford the corresponding triazole, 1,2-diazole, and isoxazole products. It also underwent an ene reaction with β-pinene that showed anomalous regiochemistry compared to other acetylenic sulfones. The Diels−Alder cycloadducts obtained from the reaction of 1 with 2,3-dimethyl-1,3-butadiene and 1,3-cyclohexadiene were readily converted into the corresponding β-keto sulfones and ketones, thus rendering 1 as the synthetic equivalent of p-toluenesulfonylketene and ketene, respectively. Base-catalyzed elimination of TsOH from the Diels−Alder cycloadduct obtained with 2,3-dimethyl-1,3-butadiene afforded the corresponding aryl phenyl selenide, while the adduct from piperylene underwent oxidation to its selenoxide, followed by a Pummerer-type reaction to produce 2-(phenylseleno)-3-(p-toluenesulfonyl)toluene. The reaction of the bicyclic Diels−Alder product obtained from 1,3-cyclohexadiene with MeCu(SePh)Li resulted in substitution of the phenylseleno moiety by a methyl group, whereas similar treatment of the monocyclic adduct derived from piperylene effected elimination of PhSeH and aromatization.

Abstract:The Baylis-Hillman reaction of acrylonitrile, methyl acrylate, and acrolein with several cyclic adicarbonyl compounds was investigated. Whereas acrylonitrile reacted with most of these ketones, giving good yields of the expected 1'-cyanovinyl carbinols, the more sterically demanding methyl acrylate failed to undergo the reaction. Attempted Baylis-Hillman reaction of acrolein with the 1,2-dicarbonyl substrates usually resulted in polymers but, in two cases, the desired a-substituted acroleins were obtained. An alternative route to such compounds was developed, employing a Grignard -allylic oxidation sequence. In bioassays, some of the products, embodying the functionality believed responsible for the phytotoxicity of the sesquiterpene bipolaroxin, inhibited germination of lettuce seeds. This activity diminished with time.Key words: Baylis-Hillman, acrylonitrile, acrylate, acrolein, a-dicarbonyl, bipolaroxin, phytotoxicity.RCsumC : Nous avons ttudit la rtaction de Baylis-Hillman sur l'acrylonitrile, l'acrylate de mtthyle ainsi que l'acroltine avec plusieurs composts a-dicarbonyliques cycliques. Tandis que l'acrylonitrile rtagit avec la plupart de ces cttones, fournissant les carbinols 1'-cyanovinyliques attendus avec de bons rendements, l'acrylate de mtthyle, h cause de sa plus grande exigence sttrique, ne rtagit pas de tout. Quand la rtaction de Baylis-Hillman fut essayte avec l'acroltine et les composts a-dicarbonyliques, seulement des polymbres furent obtenus l'exception de deux cas, oh les acroltines a-substitutes furent obtenues. Utilisant la rtaction de Grignard, suivie d'une oxidation allylique, une autre route pour produire ces composts fut developpte. Quelques-uns de ces produits, posstdant la structure partielle que I'on croit responsable de la phytotoxicitt du sesquiterpbne bipolaroxin, ont inhibt la germination des semences de laitue. Cet activitt a diminuC avec le temps.

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