Palladium-Catalyzed Syntheses of Conjugated Trienes

Steroids: reactions and partial synthesis

“…Conversion of ( 62)-tacalciol into calciol at 20 "C is accelerated at high pressure (15 K bar) in various s01vents.l~~ Rate constants are 3-5 times larger than the corresponding rate constants at 1 bar. A concerted [ 1,7] sigmatropic hydrogen shift mechanism is indicated by AVt of -5.14 cm3 mol-' or lower, by analogy with the values obtained for concerted [1,5] sigmatropic shifts. The significant rate increase, together with the quantitative recovery, is of potential use in the production of calciol analogues when the [1,7] hydrogen shift is slow, or when the compounds are thermally labile.…”

“…A concerted [ 1,7] sigmatropic hydrogen shift mechanism is indicated by AVt of -5.14 cm3 mol-' or lower, by analogy with the values obtained for concerted [1,5] sigmatropic shifts. The significant rate increase, together with the quantitative recovery, is of potential use in the production of calciol analogues when the [1,7] hydrogen shift is slow, or when the compounds are thermally labile. Kinetic studies of this type of shift in the transformation of 3-deoxy-1 -hydroxy-(6Z)-tacalciol epimers to 3-deoxy-1 -hydroxycalciol show a primary deuterium kinetic isotope effect of approximately 6.…”

“…The iodoxybenzene method for the direct oxidation of 5pcholan-3a-01s to 1,4-dien-3-ones has been applied to a wider range of cholanoic esters.6 The oxidation involves the use of benzene seleninic anhydride as catalyst in refluxing toluene, and good yields are obtained when hydroxyl groups in rings B and c are protected. Both 6-and 7-hydroxy esters give complex mixtures of products, whereas methyl deoxycholate (1) gives the 1,4-diene-3,12-dione (2) cleanly. N,N'-Sulphinyldiimidazole, prepared from imidazole and thionyl chloride, can be used to dehydrate steroidal alcohol^.^ Thus, the 1 lp-alcohol(3) is converted into the dienedione (4) in 45% yield by brief reaction in tetrahydrofuran at room temperature.…”

Synthesis of Diphenylhexatriene by the Pd-Catalyzed Dimerization of Cinnamyl Acetate

“…4 Kasahara and coworkers discovered the palladium-catalyzed coupling of fumaryl chloride ( 9 ) with styrene ( 10 ) to provide 1 in 44% yield. 5 Two methods to directly convert cinnamaldehyde ( 12 ) to DPH ( 1 ) in good yields have also been reported. A titanium-catalyzed dimerization furnished DPH ( 1 ) in 65% yield, as recently shown by the Barrero group.…”

Regio- and Stereoselective Dimerization of Terminal Alkynes to Enynes in InCl3-NaBH4-MeCN System

“…Palladium-catalyzed vinylation of phenylpropioloyl chloride can also give enynes. 6 Recently the organoindium compounds were explored gradually and have been applied in organic synthesis more and more widely. [7][8][9][10] In this paper we wish to present a novel synthesis to (E)enynes by the head-to-head dimerization of terminal alkynes in a mild and nontoxic system in a one-pot reaction.…”