Science of Synthesis

Kündig, E. P.; Pache, S. H., Science of Synthesis, (2003) 2, 207.

(Arene)tricarbonylchromium(0) complexes catalyze the 1,4-addition of hydrogen to 1,3-dienes, the hydrogenation of alkynes to Z-alkenes, and the isomerization of 1,4- and 1,3-dienes.[‌323‌,‌324‌] The high chemo-, regio-, and stereoselectivity of these processes make them powerful synthetic tools. All of these processes involve metal—arene bond cleavage to generate the catalytically active species [Cr(CO)3S3] (S = solvent). The most active precatalysts are therefore complexes that undergo arene displacement readily, such as tricarbon­yl(naphthalene)chromium(0) (‌14‌). Coordinating solvents (tetrahydrofuran, acetone) are best and, in tetrahydrofuran, 1,4-hydrogenation of dienes occurs slowly already at ambient temperature and ambient pressure, although slight warming (50°C) and higher pressure (40–100 bar) render the process more efficient. Tricarbonyl(methyl benzoate)chromium(0) (‌6‌, M = Cr; R1 = CO2Me) is used at ca. 120°C and has a longer induction period. The hydrogenation reaction likely involves a [Cr(H2)(CO)3(diene)] complex in which the diene adopts an s-cis conformation.[‌325‌] In the absence of hydrogen, isomerization of the diene via 1,5-hydrogen migration takes place to form the most stable diene capable of adopting a cisoid conformation.[‌324‌,‌326‌] This process, as well as that of isomerization of 1,4-dienes to 1,3-dienes, presumably occurs via [CrH(CO)3(pentadienyl)] intermediates.[‌327‌,‌328‌] 1,4-Hydrogenation of 1,3-dienes has been applied in prostaglandin[‌329‌] and in pheromone syntheses.[‌330‌] Examples shown in ‌Scheme 55‌ include the hydrogenation of methyl sorbate (‌139‌) to methyl (Z)-hex-3-enoate (‌140‌),[‌323‌] the 1,5-addition of hydrogen and C—C bond formation in norbornadiene,[‌331‌] the tricarbonyl(methyl benzoate)chromium(0) (‌6‌, M = Cr; R1 = CO2Me) catalyzed synthesis of a key reagent in the synthesis of ω–3 prostaglandins,[‌329‌] and the stereocontrol of the exocyclic alkene in a key intermediate ‌142‌ of a prostacyclin analogue.[‌332‌] (Arene)tricarbonylmolybdenum(0) and (arene)tricarbonyltung­sten(0) complexes give products of low regio- and stereoselectivity in this transformation, and ligand substitution in the tricarbonylchromium group often leads to loss of activity. One exception to this is the methyl acrylate complex ‌130‌.[‌268‌]

‌Meeeee 88‌ (Meeee)eeeeeeeeeeeeeeeeeee(8) Meeeeeeee ee Meeeeeeeeeeee Meeeeeeee ee 8,8-Meeeee[‌888‌,‌888‌,‌888‌,‌888‌]

Meeee eeeeeeeeeee eeeeeeeeee eeeeee eeee eee eeeeeeeeeeee ee M-eeeeeee ee (eeeee)eeeeeeeeeeeeeeeeeee(8) eeeeeeeee eee eeeeee eeeeeee ee eeeeeeee e eeeeee eeeeeeeeeeee eee eeeeeee (‌Meeeee 88‌).[‌888‌]

‌Meeeee 88‌ (Meeee)eeeeeeeeeeeeeeeeeee(8) Meeeeeeee ee Meeeeeeeeeeee Meeeeeeee ee ­Meeeeee eee Meeeee[‌888‌]

(Meeee)eeeeeeeeeeeeeeeeeee(8) eeeeeeeee eeee eeeeeeee eee eeeeeeee ee eeeeee eeeeeeeeeeeee ee eeeeeee[‌888‌] eee eee eeeeeeeeeeeeeeeeeee ee eeeee eeeeeee.[‌888‌] Meeeeeeeeee(eeeeeeeeeee)eeeeeeee(8) (‌88‌) eeeeeeeee eee [8π + 8π]-eeeeeeeeeeeee eeeeeeee eeeeeee eeeeeeeeeeeeeeee eee eeeee eeeeeeee.[‌888‌,‌888‌]

(Meeee)eeeeeeeeeeeeeeeeeee(8) eeeeeeeee eee eeee eeeeeeeeeeeeeee eee eee eeeeeee eeeeeeeeeeeeee ee eeeeeeeee[‌888‌,‌888‌] ee eee eeeeeeee ee eeeeee eeeeeeeeeeeee. Meee eeeeeee eeeeeeeeee ee eeeeeeeee ee e eeeeeeeeee eeeeeeee–eeeeeeee eeeeeeee eeeeeeee ee eeeee eeeeeeeeeeee (eee Meeeeee ‌8.8.8‌).

Meeeeeeeeeee Meeeeeeee

(8M,8M,8M,8M)-8-{[(eeee-Meeeeeeeeeeeeeeeee)eee]eeeeee}-(M)-8-(8-eeeeeeeeeeeeeeeee)-8-[(eeeeeeeeeeeeeeeee)eee]eeeeeee[8.8.8]eeeeee (‌888‌):[‌888‌]

Mee eeeeee eeeeeee ‌888‌ (888 ee, 8.88 eeee) eee [Me(MM)8(eeeeeeeeeee)] (‌88‌; 88 ee, 8.88 eeee) eeee eeeeeeeee ee MMM (88 eM). Meeee eeeeee eeeeeeeeeeeee ee eeeee eeeeee–eeee–eeee eeeeee, eee eeee eee eeeeee ee 88°M eeee eeeeeeee eeeee ee eeeeeeeeee ee M8 (888 eee eeeeeeee) eee 88 e eee eeeeeeeeeeee. Mee eeeeeee eee eeeeeeee ee eeeeee eeeeeeeeeeeeee (eeeeee eee, Me8M/eeeeee 8:8) ee eeee eee eeeeeee eeeeeee (888 ee, 88%) ee e eeeeeeeee eee. Me e eeeeeee eeee ee eee eeeeeee (888 ee, 8.88 eeee) ee MeMM (8.8 eM) eee eeeee eeeee M8MM8 (88 ee, 8.8 eeee) ee ee eee eee eeeeeeeee eeeeeeeeee eee eeeeeee ee ee eee 88 eee eee eeeeeeeeeeee. Mee eeeeeee eee eeeeeeee ee eeeeee eeeeeeeeeeeeee (eeeeee eee, Me8M) ee eeeeee ‌888‌ ee e eeeeeeeee eee; eeeee: 88 ee (88%); 8M MMM (MMMe8, δ): 8.88 (e, 8M), 8.88 (e, 8M), 8.88 (e, M = 8 Me, 8M), 8.88 (e, 8M), 8.88 (ee e, M = 8.8 Me, 8M).

References

Meeeeee Meeeeeeeeee

• 8.Meeeee-Meee, (8888) M 88e, 8888.