Lewis acid catalyzed ene reactions of ethynyl p-tolyl sulfone

Abstract

Ethynyl ,D-tolyl sulfone undergoes EtAlC12-catalyzed ene reactions with alkenes to give 1,4dienyl p-tolyl sulfones in good yield.We have recently described the Lewis acid catalyzed ene and [2 + 21 cycloaddition reactions of ethynyl esters and ketones with alkene^.^^^ Depending on the substitution pattern of the alkene, good yields of ene adducts and/or cyclobutenes are obtained at 25 "C. The adducts which result from these reactions have been used for the syntheses of the A1 component of the female sex pheromone of the California red scale4 and of novel insideinside bicyclic ~ompounds.~ We report here tbe analogous reactions of ethynyl sulfones with alkenes (Scheme I). The reaction introduces a functionalized two-carbon fragment, a vinyl sulfone, which is a versatile synthon.6 The results of EtA1C12-catalyzed reactions of ethynyl p-tolyl sulfone (1) with alkenes are shown in ' Table I. These reactions proceed at 25 OC in benzene or other aromatic solvents. The reaction proceeds best for highly substituted, i.e., electron rich, alkenes. Good yields of ene adducts are obtained from all alkenes with at least one disubstituted carbon. Monosubstituted alkenes give low yields of ene adducts while l12-disubstituted alkenes give low yields of a mixture of ene adduct and cyclobutene. A similar propensity for l12-disubstituted alkenes to give cyclobutenes was observed with methyl propiol.ate2 and 3-butynoneS3This reaction is very susceptible to changes in conditions. Use of CH2C12 as solvent or AlC13 as Lewis acid results in complex mixtures of products. The stabilization of the 1.EtAlC12 complex by aromatic solvents and the ability of EtAlC12 to act as a proton scavenger minimize the side reactions. However,, even under optimal conditions, methylenecyclohexane is slowly isomerized to l-methylcyclohexene so that inixtures of 5,6, and 7 are formed. In all cases just under 1 equiv of EtA1Cl2 is used since the Table I. Adducts from the EtAlC1,-Catalyzed Reactions of Ethynyl p-Tolyl Sulfone (1 ) with Alkenes 0 9 ( 1 l ) b 8 (20)b (1) Fellow of the Alfred P. Sloan Foundation, 1979-1981. (2) Snider, B. B.; Rodini, D. J.; Conn, R. S. E.; Sealfon, S. J. Am. Chem. SOC. 1979,101,5283. Snider, B. B.; Roush, D. M.; Rodini, D. J.; Gonzalez, D.; Spindell, D.Consists of 80% 7 and 20% of a 3 : l mixture of 5 and 6.obtained. X = p-tolylsulfonyl.product akenyl sulfone is more basic than 1 and complexes preferentially to EtAlCl,.' A 19% yield of 14 and cyclohexyl benzene were also

Cycloaddition Reactions of 1-Phenylseleno-2-(p-toluenesulfonyl)ethyne

“…Acetylenic sulfones are also known to undergo Lewis acid-catalyzed ene reactions. 2m, We observed that the treatment of β-pinene with 1 afforded the ene reaction product 23 in the absence of a Lewis acid, as shown in Scheme . Only the one regioisomer, tentatively identified by NOE experiments and by the chemical shift of the olefinic proton of the β-(phenylseleno)vinyl sulfone moiety, was isolated.…”

The synthesis of diethyl p-tolylsulphonylethynylphosphonate and related acetylenes, and their reactions with nucleophiles, pyridinium-1-dicyanomethylides, and dienes

“…This compound (1.0 g) in ethanol (20 ml) was treated with potassium hydroxide (0.3 g) when a precipitate formed immediately. The mixture was stirred for 30 min after which water (50 mi) was added and most of the ethanol evaporated off; extraction of the residue with ether and distillation yielded the title compound (10) (20), 175 (25), 148 (loo), and 147 (50).…”

Synthesis of Alkynyl Sulfones

“…Hydrogen peroxide and m‐ chloroperoxybenzoic acid ( m‐ CPBA) are commonly used oxidizing agents in this technique. Currently, these two oxidizing reagents remain the most used for this purpose (Scheme ) . Peroxybenzoic acid and peroxyethanoic acid have also been used for this purpose, although to a lesser extent.…”