PREPARATION AND REDUCTIVE

PREPARATION AND REDUCTIVE CLEAVAGE OF ENOL PHOSPHATES 5-METHYLCOPROST-3-ENE... 

Two of these methods, the Gabriel synthesis and the preparation and reduction of the corresponding azide, begin with ethyl bromide. 

Conversion of o-fluoroanisole to 4-amino-2-fluoroanisole proceeds in the conventional way by preparation and reduction of a nitro derivative. Once the necessary arylamine is at hand, it is converted to the nitrile by a Sandmeyer reaction. 

C. Preparation and reductive cleavage of the vinyl phosphoroimi-date. A dry, 250-mL flask equipped with magnetic stirrer, syringe port (Note 9), and argon outlet is flushed three times with argon. To the flask... 

The acid or base elimination of a diastereoisomerically pure p-hydroxysilane, 1, (the Peterson olefination reaction4) provides one of the very best methods for the stereoselective formation of alkenes. Either the E- or Z-isomer may be prepared with excellent geometric selectivity from a single precursor (Scheme 1). The widespread use of the Peterson olefination reaction in synthesis has been limited, however, by the fact that there are few experimentally simple methods available for the formation of diastereoisomerically pure p-hydroxysilanes.56 One reliable route is the Cram controlled addition of nucleophiles to a-silyl ketones,6 but such an approach is complicated by difficulties in the preparation of (a-silylalkyl)lithium species or the corresponding Grignard reagents. These difficulties have been resolved by the development of a simple method for the preparation and reductive acylation of (a-chloroalkyl)silanes.7... 

The imines thus formed are often not isolated but are, instead, reduced directly to amines. Although NaBH3(CN) is a very common reducing agent, NaBH4 or other reagents shown in Table 23 can also be used. When preparation and reduction of the imine are performed successively in the same apparatus, Ti(0-/-Pr)4 seems to be a more suitable reagent than TiCU for imine formation (Eq. 249) [573]. Preparation of several amines by use of this sequence is shown in Table 23. 

Beau, J M, Sinay, P, Preparation and reductive lithiation of 2-deoxy-D-glucopyranosyl phenyl sulfones a highly stereoselective route to C-glycosides, Tetrahedron Lett., 26, 6185-6188, 1985. Crich, D, Lim, L B L, Synthesis of 2-deoxy-(3-C-pyranosides by diastereoselective hydrogen-atom transfer. Tetrahedron Lett., 31, 1897-1900, 1990. 

The details of preparation and reduction of the Co-ThOj-MgO-kieselguhr catalyst are described in CIOS reports (41-49) and other publications (34, 35, 36). A solution of cobalt and thorium nitrates is mixed with sodium carbonate solution so as to completely precipitate the cobalt and thorium carbonates. A slurry of magnesium oxide and kieselguhr is... 

The reaction of o-H2(TAmPP) (129) with excess isonicotinic chloride hydrochloride yielded the tetra-isonicotinamide TPP as a statistical mixture of atropisomers which could be separated by chromatography. The isonicotinamide groups were then methylated with CH3I, followed by anion exchange, to yield the water soluble tetrakis-(N-methyl-isonicotinamidophenyl)porphyrin-tetracation (138) (Scheme 39). The corresponding para and meta derivatives were also prepared and reduction potentials, basicity and reactivity with metal ions of the isomers were compared ... 

Details have been published of Boekelheide s synthesis of [2,2]metacyclophane-1,9-dienes methylation on sulphur of the bis-sulphide (44), Stevens rearrangement, methylation again, and Hoffmann elimination, gave the dimethyl[2,2]metacyclo-phane-1,9-diene (45), which could be isomerized reversibly to trans-15,16-dimethyl-dihydropyrene. [2,2]Metaparacyclophanes and [2,2]metaparacyclophane-l,9-dienes were prepared by similar methods. A second synthesis of [2,2]metaparacyclo-phanes involves preparation and reduction of bis-dithianes, e g. (46), and a third synthesis involved pyrolysis of bis-sulphones obtained by oxidation of disulphides analogous to (44). Ring flipping in substituted [2,2]metaparacyclophanes and... 

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