Selective reductions. XX. Stereochemistry of the reduction of cyclic, bicyclic, and polycyclic ketones by dialkylboranes. Simple, convenient procedure for the reduction of ketones to the corresponding alcohols with exceptionally high steric control

Abstract

state, 29, predominant formation of the cis decalin 27 would be expected. As shown for 3 in diagram 21, the Ci equatorial hydrogen bond in 26 is perpendicular to the cyclopropane bond which is adsorbed on the catalyst. Thus, the formation of the olefin 30 could occur by a process similar to that described for the formation of 22. While the product stereochemistry obtained from the hydrogenation of 30 is not available, it has been reported that the hydrogenation of the demethyl compound 31 over platinum in acetic acid at room temperature and 1 atm gives a 60:40 mixture of the cis and trans decalins 32 and 33.18 Further work is currently underway in an attempt to establish whether the hydrogenolysis of cyclopropyl compounds such as 3 and 26 does, indeed, take place through an olefin intermediate as proposed here.

Zn-Catalyzed Multicomponent KA2 Coupling: One-Pot Assembly of Propargylamines Bearing Tetrasubstituted Carbon Centers

“…As shown in Figure , the obtained compound could be either endo - 4h or exo - 4h . Based on the related literature, nucleophiles tend to add to norbornanone from the exo side, giving very high diastereoselectivities. , The same also applies to alkynyl-metal reagents. , A combination of 1 H NMR, 13 C NMR, 1 H, 1 H-COSY, 1 H, 13 C-HSQC, and 1 H, 1 H-NOESY spectroscopies (see Supporting Information) leads to the conclusion that the piperidine unit resides on the endo side of the molecule. Because of the complexity of the acquired spectra, our conclusion is not definitive, but in conjunction with the known propensity of nucleophiles to add to norbornanone from the exo side, the data suggest exo alkynylation.…”

“…Based on the related literature, nucleophiles tend to add to norbornanone from the exo side, giving very high diastereoselectivities. 18a,60 The same also applies to alkynyl-metal reagents. 61,62 A combination of 1 H NMR, 13 C NMR, 1 H, 1 H-COSY, 1 H, 13 C-HSQC, and 1 H, 1 H-NOESY spectroscopies (see Supporting Information) leads to the conclusion that the piperidine unit resides on the endo side of the molecule.…”

Cerium(III) Chloride-Mediated Stereoselective Reduction of a 4-Substituted Cyclohexanone Using NaBH4

“…Several methods have been developed for the stereoselective reduction of ketones, especially substituted cyclohexanones. − In general, the thermodynamically less stable axial alcohols arising from an equatorial delivery of the hydride may be accessed by the use of bulky hydride-based reducing agents . In our case, the desired product was the equatorial alcohol, which would be formed via axial delivery of the hydride.…”

Preparation of chiral trans-2,4-dimethyl-1-cyclohexanones, the key intermediates in cycloheximide synthesis, using microbial resolution.

“…Already, we have demonstrated that microbial hydrolysis of ( ± )-t-2,t-4-dimethyl-r-l-cyclohexyl acetate, followed by the oxidation, gave (-)-(2/?,4/? )-c/s-2,4-dimethyl-l-cyclohexanone (6).2) Here, we describe a synthetic method for chiral trans-2,4-dimethy\-1-cyclohexanone (2) by using the microbiological system. The condensation of 4-methyl-l -cyclohexanone (4) with pyrrolidine gave the enamine 5, which was reacted with methyl iodide to form a stereoisomeric mixture of( + )-2,4-dimethyl-1-cyclohexanones.…”

“…14% of (±)-cisketone (6 2) Reduction of (+ )-2,4-dimethyl-l-cyclohexanone with K-seleetride. To a stirred solution of (±)-2,4-dimethyl-1-cyclohexanone (1.92 g) in 20ml of dry THF at -30°C was added 28 ml ofa 1 m solution ofK-selectride in THF, stirring being continued for 2 hr.…”