The first selective linear codimerization of terminal acetylenes and 1,3-dienes catalyzed by dihydridotetrakis(trialkylphosphine)ruthenium complexes

Abstract

Preparation of Z-Ala-OCH3. To a solution of N-(benzyloxycarbonyl) alanine (447 mg, 2.0 mmol) and triethylamine (213 mg, 2.1 mmol) in methylene chloride (6 mL) at 0 °C was added methyl chloroformate (190 mg, 2.0 mmol). After 10 min of stirring at 0 °C, DMAP (23 mg, 0.2 mmol) was added and the resulting solution was stirred at 0 °C for 15 min. The reaction mixture was diluted with methylene chloride (40 mL) and washed with saturated NaHC03 (20 mL), 0.1 M HC1 (10 mL), and saturated NaCl (30 mL). The aqueous layers were extracted with methylene chloride (20 mL). The combined extracts were dried over anhydrous MgS04 and evaporated to dryness. The residue was subjected to silica gel column chromatography with methylene chloride as an eluant to yield pure Z-Ala-OCH3 (455 mg, 96%):

Iridium‐Catalyzed Enantioselective Hydroalkynylation of Enamides for the Synthesis of Homopropargyl Amides

“…Enamides with an acetal, ketone, and ester group underwent the hydroalkynylation smoothly (3 r-t), thus furnishing valuable homopropargyl amides in good enantioselectivity except for the ester-containing product 3 t. As in many catalytic hydroalkynylation reactions, the alkynes are currently limited to silylacetylenes. [8][9][10][11] Aryl-and alkyl-substituted terminal alkynes did not react under the current reaction conditions because of fast oligomerization of these alkynes.…”

“…[6,7] Recently,c atalytic asymmetric hydroalkynylation of electron-neutral alkenes was developed, but the only applicable substrates are 1,3-dienes, [8] allenes, [9] and norbornene. [10,11] A catalytic hydroalkynylation of electron-rich alkenes remains undeveloped. Moreover,b ecause the b-position of an enamide is more electron-rich than the a-position, a b-selective alkynylation process would require the catalyst to effectively overcome the intrinsic electronic requirement for the acetylide addition.…”

Efficient Isomerization of Allylic Alcohols to Saturated Carbonyl Compounds by Activated Rhodium and Ruthenium Complexes

“…A change in ligand was also investigated. For example, the replacement of the triphenylphosphane for tri-n-butylphosphane resulted in an active catalyst 15 with comparable results, [10] in spite of the difference in steric and electronic factors between the two ligands. With the additive K 2 CO 3 (entry 10), we obtained only a low yield and a slow rate of conversion contrary to the literature report.…”

Synthesis and structure of [Ru(dppe)2(CH3CN)Cl][BPh4] and its catalytic application to anti-Markovnikov addition of carboxylic acids to terminal alkynes

“…Ruthenium catalyzed addition of carboxylic acid has been studied extensively by Dixneuf and coworkers [27,32,33] and Mitsudo and coworkers [29e31] and catalytic systems for antiMarkovnikov addition as well as Markovnikov addition product have been developed. For anti-Markovnikov addition, the catalysts used were synthesized from sensitive organometallic compounds like, bis(cyclootadienyl)Ru [29,30] or bis(2-methylpropenyl)-(cyclooctadienyl)Ru [27]. Recently Goossen et al have reported anti-Markovnikov addition of carboxylic acid to alkynes using [(pcumene)RuCl 2 ] 2 and phosphenes like PPh 3 , P(Fur) 3 , or P(p-Cl-C 6 H 4 ) 3 in the presence of organic bases like pyridine or (4-dimethylamino)pyridine [28].…”