α-Phenylselenenylation of zirconium or aluminum enolates

Asymmetric Synthesis of the Epimeric (3S)-3-((E)-Hex-1-enyl)-2-methylcyclohexanones

“…In our case, the 1,4-addition was performed on 2-cyclohexenone using (E)-1-hexenylzirconocene chloride [6], prepared from 1-hexyne and bis(cyclopentadienyl)zirconium chloride hydride (Cp 2 Zr(H)Cl or Schwartz reagent) in the presence of a catalytic amount of the Rh(I)-complex [Rh(cod)Cl] 2 and (R)-BINAP as a chiral ligand. As previously observed by Schwartz, we were unable to directly alkylate the intermediate zirconium O-enolate [7]; however, reaction with gaseous formaldehyde at -78 °C led, after acid work-up, to a 2.7:1 mixture (89% yield) of 1a and 1b, respectively [8], with an excellent ee (better than 96%) [9]. The obtained mixture was readily separated by flash chromatography.…”

Production of detoxified sorghum straw hydrolysates for fermentative purposes

“…Moreover, analysis of the reaction mechanism by NMR revealed quantitative transmetalation of the enolates from zirconium to lithium upon MeLi addition. This observation may lead to the development of further types of trapping reactions besides the aldol25 and selenylation26 reactions already known and the silylation presented herein. Moreover, the range of alkynes employed in this reaction was enlarged and the efficiency of the catalyst was demonstrated by the synthesis of a cis ‐3,5‐disubstituted cyclohexanone.…”

“…Unfortunately, such zirconium enolates offer only a limited scope of subsequent transformations. Aldol reactions25 as well as α‐selenylation26 have been achieved, yet it is impossible to introduce an alkyl or allyl group by nucleophilic substitution 17d,25a,26. On the contrary, Oi, Inoue et al.…”

Development of Analogues of 1α,25‐Dihydroxyvitamin D3 with Biased Side‐Chain Orientation: C20 Methylated Des‐C,D‐homo Analogues

“…It features the highly enantioselective 1,4‐addition of an alkenylzirconocene chloride to 2‐cyclohexenone by a chiralrhodium(I) complex generated with BINAP as chiral ligand, a methodology which has led to the synthesis of enantiomerically pure 16 13. In our case, the 1,4‐addition was performed by using ( E )‐1‐hexenylzirconocene chloride,prepared from 1‐hexyne and Cp 2 Zr(H)Cl (Schwartz reagent)14 in the presence of a catalytic amount of the rhodium(I) complex [Rh(cod)Cl] 2 and ( R )‐BINAP, followed by trapping of the O‐enolate with formaldehyde 15. This led to a 7:3 mixture (95 %) of 17a / 17b with an excellent ee value (better than 96 %).…”

“…IR: ν ˜= 2952 (vs), 2876 (s), 2831 (m), 2240 (vw), 1739 (vs), 1542 (vw), 1451 (m), 1375 (m), 1313 (m), 1244 (s), 1165 (vs), 1078 (s), 1037 (vs), 954 (m), 926 (m), 740 (s) cm -1 . MS: m/z (%) = 425 (14), 335 (5), 219 (4), 191 (8), 159 (17), 143 (6), 117 (17), 87 (10), 75 (100), 47 (19) MS: m/z (%) = 398 (9), 365 (5), 307 (5), 199 (6), 159 (13), 131 (4), 107 (9), 89 (15), 75 (100), 47 (14).…”