Selected reductions using

SL Selected Reductions Using Metal Redactor Columns... 

Selective reduction. Use of reagent, generated by cupric ion-catalyzed air oxidation of hydrazine, for the preparation of m-cyclododecene by the selective reduction of cis.trans.trans-1,5,9-cyclododccatriene, the product of trimerization of butadiene,7-8 is described by Ohno and Okamoto9 (see also 1,258, ref. 10). 

In the triene series for the synthesis of the stereoisomers of (15 3)-anacardic acid, namely the 8(Z),11(Z),14 8(E),11(E),14 8(Z),11(E),14 and 8(Z),11(E),14 compounds by the alkylation of the ArC., intermediate (ethyl 2-methoxy-6-methybenzoate) with a 0 4 component these boration methods have been of value as an addition to selective catalytic hydrogenation and the use of terminal trimethylsilylation (ref. 167). At this stage for synthetic purposes the selective reductive use of boration methods has been mainly exploited. The chief use of combined addition/alkylation procedures is for obtaining 8(E), and 11 (E) isomers. For this, the sequence of synthons, for the side chain has to follow the different series, Ar9->ArCi2->ArCi5. 

Njardarson and coworkers utilized the Cu-catalyzed ring expansion of thiiranes developed in their lab as the key step in syntheses of the cores of Biotin and Plavix tSchemes 11.62 and 11.63). The vinylthiirane precursor 102 for Biotin s core was prepared by cross metathesis of ethyl 6-heptenoate 100 with enone thiophosphate 101, followed by selective reduction using NaBH4 and subsequent cyclization (Scheme 11.61T Rearrangement of 102 using 5 mol% Cu(hfacac)2 in benzene afforded dihydrothiophene 103 in high yield and can be converted to Biotin in a few steps tScheme 11.62T ... 

ATH can be used to form sultams (Fig. 15) in a very efficient and selective reduction using Ru complexes [70] indeed, this was one of the first reported applications of the Ru(II)/arene/TsDPEN complexes. Analogous Rh(III) complexes can also be used [25]. 

C. F. Lane, Selective Reductions Using Metal Hydrides , in Aspects of Mechanism and organometallic Chemistry , ed. J. H. Brewster, Plenum Press, New York, 1978, p. 181. 

The TBIN 38 was made (Scheme 18) frornhydroxynitrile 25 (13,14) which was described earlier. Chain elongation was accon lished through the anion of t-butyl acetate addition to 25. Selective reduction using triethyl borane and borohydride introduces the second chiral center. Unfortunately, or fortunately, this required low tenq>erature equipment which was not in the stable of normal manufacturing equipment. At least one year was expended trying to run the reaction at warmer tenq>erature. The reaction would go, but the yield was very poor. The formation of lithium t-butyl acetate 39 is run at low tenq)erature, and 25 is added to form the hydroxy ketone 40. But most inq>ortant was the correct... 

Lithium aluminium hydride LiAlH is a useful and conveuient reagent for the selective reduction of the carbonyl group and of various other polar functional groups. It is obtained by treatment of finely powdered lithium hydride with an ethereal solution of anhydrous aluminium chloride ... 

Very selective c/s-hydrogenations are also achieved by reduction with diiminc (N2H2, S. Hiinig, 1965 C.E. Miller, 1965 D.J. Pasto, 1991). The reagent can be used at low temperatures and has been employed in the selective reduction of C C double bonds, e.g. in the presence of a sensitive peroxidic function (W. Adam, 1978). 

Addition of dihydrosilane to a, /J-unsaturated carbonyl compounds such as citral (49), followed by hydrolysis, affords saturated citroneJlal (50) directly. The reaction is used for the selective reduction of conjugated double bonds[45,46]. In addition to Pd catalyst, the use of a catalytic amount of... 

Formic acid is a good reducing agent in the presence of Pd on carbon as a catalyst. Aromatic nitro compounds are reduced to aniline with formic acid[100]. Selective reduction of one nitro group in 2,4-dinitrotoluene (112) with triethylammonium formate is possible[101]. o-Nitroacetophenone (113) is first reduced to o-aminoacetophenone, then to o-ethylaniline when an excess of formate is used[102]. Ammonium and potassium formate are also used for the reduction of aliphatic and aromatic nitro compounds. Pd on carbon is a good catalyst[103,104]. NaBH4 is also used for the Pd-catalyzed reduction of nitro compounds 105]. However, the ,/)-unsaturated nitroalkene 114 is partially reduced to the oxime 115 with ammonium formate[106]... 

Fig. 7. NO reduction using selective catalytic recovery (SCR) (a) basic principles of the SCR process where represent gas particles and (b) effect of...

The Corey process is also useful for the synthesis of PGs of the 1 and 3 series. Catalytic hydrogenation of (34) (see Fig. 5) with 5% Pd/C at — 15-20°C results in selective reduction of the 5,6-double bond. Subsequent transformations analogous to those in Figure 5 lead to PGE (9) and PGF (10). The key step for synthesis of the PG series is the Wittig reaction of (29) with the appropriate unsaturated CO-chain yUde (170). 

The aromatic primary and secondary stibines are readily oxidized by air, but they are considerably more stable than their aHphatic counterparts. Diphenylstibine is a powerful reducing agent, reacting with many acids to Hberate hydrogen (79). It has also been used for the selective reduction of aldehydes and ketones to the corresponding alcohols (80). At low temperatures, diphenylstibine undergoes an addition reaction with ketene (81) ... 

Sulfide is used for the selective reduction of dinitro compounds to nitroarylamines, and for metal-sensitive systems, such as certain substituted ... 

Me2CHCH2)2AlH, PhCH3, —78°, 80% yield. Since the /V-benzoyl group in this substrate could not be removed by hydrolysis, a less selective reductive cleavage with diisobutylaluminum hydride was used. 

In the early work on the synthesis of prostaglandins, zinc borohydride was used for the reduction of the 15-ketone function and a 1 1 mixture of epimeric 15(S)- and 15(/ )-alcohols was generally obtained. Subsequent studies led to reaction conditions for highly selective reduction to the desired 15(S)-alcohol. Some of the results are summarized in the following table. The most practical method is E which utilizes borane as the stoichiometric reductant and a chiral, enzyme-like catalyst which is shown. 

---