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Homogeneous catalytic hydrogenation of carbonyl groups is a synthetically useful and widely applied organic transformation. Sustainable chemistry goals require replacing conventional noble transition metal catalysts for hydrogenation by earth-abundant base metals. Herein, we report how a practical in situ catalytic system generated by easily available pincer NHC precursors, CoCl2, and a base enabled efficient and high-yielding hydrogenation of a broad range of ketones and aldehydes (over 50 examples and a maximum turnover number [TON] of 2,610). This is the first example of NHC-Co-catalyzed hydrogenation of C=O bonds using flexible pincer NHC ligands consisting of a N-H substructure. Diastereodivergent hydrogenation of substituted cyclohexanone derivatives was also realized by fine-tuning of the steric bulk of pincer NHC ligands. Additionally, a bis(NHCs)-Co complex was successfully isolated and fully characterized, and it exhibits excellent catalytic activity that equals that of the in-situ-formed catalytic system. Catalytic hydrogenation is a powerful tool for the reduction of organic compounds in both fine and bulk chemical industries. To improve sustainability, more ecofriendly, inexpensive, and earth-abundant base metals should be employed to replace the precious metals that currently dominate the development of hydrogenation catalysts. However, the majority of the base-metal catalysts that have been reported involve expensive, complex, and often air- and moisture-sensitive phosphine ligands, impeding their widespread application. From a mixture of the stable CoCl2, imidazole salts, and a base, our newly developed catalytic system that formed easily in situ enables efficient and stereoselective hydrogenation of C=O bonds. We anticipate that this easily accessible catalytic system will create opportunities for the design of practical base-metal hydrogenation catalysts. A practical in situ catalytic system generated by a mixture of easily available pincer NHC precursors, CoCl2, and a base enabled highly efficient hydrogenation of a broad range of ketones and aldehydes (over 50 examples and up to a turnover number [TON] of 2,610). Diastereodivergent hydrogenation of substituted cyclohexanone derivatives was also realized in high selectivities. Moreover, the preparation of a well-defined bis(NHCs)-Co complex via this pincer NHC ligand consisting of a N-H substructure was successful, and it exhibits equally excellent catalytic activity for the hydrogenation of C=O bonds.

A method for the convenient synthesis of the recently isolated allylic gonadal steroids, 3α-hydroxy-4-pregnen-20-one (3α-dihydroprogesterone; 3α-DHP) and 3α-hydroxy-4-androsten-17-one (3α-HA), was developed using 4-pregnene-3,20-dione (progesterone) and 4-androstene-3,17-dione as substrates and potassium trisiamylborohydride (KS-Selectride) as reducing agent. Similar reactions were also used for the reduction of 5α-pregnane-3,20-dione to 3α-hydroxy-5α-pregnan-20-one (3α-HP). The yields were about 15%, 50%, and >90% for 3α-DHP, 3α-HA and 3α-HP, respectively. Structures of the products, including the 3β-isomers and the 17α-epimer, formed in these reactions were determined by NMR and mass spectroscopic methods.

Reaction of cross-linked chloromethylated polystyrenes with 3-mercaptopropane-1,2-diol and sodium hydroxide under phase-transfer conditions gave polymers containing diol residues.A range of aldehydes and ketones were successfully bound to these polymers via acetal formation.The aldehydes and ketones were released by treating the products with aqueous dioxane in the presence of toluene-p-sulphonic acid.The polymer-supported diol could be used to isolate aldehydes or ketones from mixtures with other compounds and to separate a 3-oxosteroid from a 17- or a 20- oxosteroid.The supported diol was successfully used to protect the aldehyde group of undec-10-enal whilst the terminal vinyl group was transformed into -CH2CH2OCOPh.Attempts to monoprotect dicarbonyl compounds were unsuccessful.

The reduction of Δ4-androsten-3,17 dione 1 and of progesterone 2 by nBu4NBH4 is highly chemisoselective: in THF only the α-enone moiety is reduced, the saturated C17 or C20 keto group being kept unchanged.When TMEDA is added, saturated alcohols are obtained, without any allylic alcohol when the reaction goes to completion.However this reduction is poorly stereoselective as 70:30 mixtures of A/B cis and trans ring junction compounds are obtained.In MeOH, the saturated keto group is more than 90percent selectively reduced.However, the reduction of 1 and 2 by LiBH4 and Zn(BH4)2 is poorly chemioselective.These results are interpreted in terms of competition between electrophilic assistance and steric effects.

Zinc bis-tetrahydroborate forms a solid complex with dimethylformamide (DMF) of composition, Zn(BH4)2*1.5DMF.Unlike zinc bis-tetrahydroborate itself, the complex with DMF can be stored as a solid at room temperature.Ketones and aldehydes are reduced to the corresponding alcohols by the complex but the mechanism of reduction appears to be different from that using zinc bis-tetrahydroborate itself and from other tetrahydroborates in that only one hydride equivalent from each BH4- unit is utilized and not four.Further, although saturated aliphatic ketones are reduced rapidly to alcohols, aromatic ketones react much more slowly and α,β-unsaturated ketones react very slowly so that the complex appears to have selective reducing potential with regard to different classes of ketones.It is also apparent that the zinc bis-tetrahydroborate/DMF complex reduces sterically hindered saturated ketones much more slowly than it does unhindered ketones.An analogous cadmium bis-tetrahydroborate/DMF complex can be prepared in solution and reacts with ketones similarly to the zinc complex.

Cholesterol side chain cleavage is determined by means of separation of (26-14C)-cholesterol and its radioactively labeled side chain (1-14C)-isocaproic acid.Alumina minicolumn assay (AMCA): adsorption of cholesterol from an aqueous phase by aluminium oxide, while isocaproic acid can percolate through the column.In modification of a previously described technique, cholesterol is quantitatively eluted by ethanol.Filter assay (FA): retention of cholesterol by a membrane filter (pore size =/ 0.1 μm) while isocaproic acid can pass the filter.Two-phase scintillation assay (TPSA): pH-dependent partition of isocaproic acid between an organic scintillation mixture and an aqueous phase.The TPSA can be applied for all enzymatic reactions in which the polarity of the radioactive residue which is split off depends on pH values or when the total charge of apolar molecule is changed to an apolar state by cleaving one non-radioactive group (e.g. steroid sulfates) and vice versa.The criteria of reliability of the test systems are described.Bovine adrenal mitochondria were incubated and the side chain cleavage of (26-14C)-cholesterol was studied by the new test systems and compared to the conversion rates of (4-14C)-cholesterol to its metabolites as determined by thin layer chromatography.A good agreement of all tests was found.