Starting materials Commercially available

Compound 10 has been synthesised utilising as a starting material commercially available 4-amino-3-hydroxybenzoic acid 10a (Scheme M). 

In 1993, we reported that various unsaturated heterocycles can be alkylated with Et-, wPr- and nBuMgCl in the presence of optically pure (EBTHI)ZrCl2 (3a) or (EBTHI)Zr-binol (3b) to afford the derived unsaturated products in >90% ee (cf. 5 6, Scheme 2) [4a]. Many of the simpler five- and six-membered starting materials are available commercially or can be prepared by established procedures. In contrast, catalytic enantioselective reactions involving unsaturated medium ring hetero cycles were not a trivial undertaking the synthesis of these olefinic substrates, by the extant methods, was prohibitively cumbersome. 

Many of the routes reported for the construction of diverse chemical libraries are often constrained by the commercial availabihty of the monomer sets used as the primary building blocks. While there are a large number of simple starting materials currently available, chemists would prefer to have ready access to more sophisticated and highly functionahzed monomer units which would lead rapidly to drug-like molecules. 

Aliphatic polyketones are made from the reaction of olefin monomers and carbon monoxide using a variety of catalysts. Shell commercialized a terpolymer of carbon monoxide, ethylene, and a small amount of propylene in 1996 under the trade name Carilon (structure 4.79). They have a useful range between the Tg (15°C) and (200°C) that corresponds to the general useful range of temperatures for most industrial applications. The presence of polar groups causes the materials to be tough, with the starting materials readily available. 

Myadera and Iwai (64CPB1338) have devised a convenient route to the bromide (139 R1 = R2 = R3 = H) starting with commercially available materials (Scheme 84). The anion formed from -y-butyrolactone by the action of sodium hydride was allowed to react with ethyl picolinate to yield the keto lactone (141) which, when heated with hydrobromic acid, undergoes decarboxylation as well as bromination, yielding the bromo ketone (139). Several substituted ethyl picolinates have been used successfully, and it has also been found that the anion of the keto lactone (141) may be alkylated. 

Chopa, A.B., Silbestri, G.F. and Lockhart, M.T. (2005) Strategies for the synthesis of bi- and triarylic materials starting from commercially available phenols. Journal of Organometallic Chemistry, 690, 3865-3877. 

A more convenient method for 1 was developed starting from commercially available Ph2SnCl2. All fluoroalkyldistannoxanes thus prepared were isolated as crystalline materials, and Sn NMR spectra gave rise to two distinct resonances diagnostic of the characteristic dimeric distannoxane formulation. 

The more convergent routes of Nicolaou et al. and Danishefsky et al. with B ring closure from a tethered A-C precursor are clearly the least efficient with respect to total yield (about 0.01 % starting from commercially available materials) if directly compared to the other two routes. Additionally the Nicolaou route needs enantiomer separation or a -presumably less favorable - asymmetric synthesis, whereas the Danishefsky route addresses absolute stereochemistry but involves more steps. Holton s synthesis shows quite good yields throughout with a total one of approximately 0,1 %, but has less room for improvements and is based on a not readily available starting material. The best synthesis in all respects to date is the one of Wender and coworkers, which is about 1-2 orders of magnitudes better in total yield (ca. 0.8%),... 

The aim of a retrosynthetic analysis is the transformation of a synthesis target into progressively simpler structures, following a pathway to commercially available starting materials. 

Each transform should lead to reagents, which are more easily accessible than the target molecule. In the subsequent steps of antithesis the reagents are defined as new target molecules, and the transform procedure is repeated until the reagents needed are identical with commercially available starting materials. 

Much more important is the hydrogenation product of butynediol, 1,4-butanediol [110-63-4]. The intermediate 2-butene-l,4-diol is also commercially available but has found few uses. 1,4-Butanediol, however, is used widely in polyurethanes and is of increasing interest for the preparation of thermoplastic polyesters, especially the terephthalate. Butanediol is also used as the starting material for a further series of chemicals including tetrahydrofuran, y-butyrolactone, 2-pyrrohdinone, A/-methylpyrrohdinone, and A/-vinylpyrrohdinone (see Acetylene-DERIVED chemicals). The 1,4-butanediol market essentially represents the only growing demand for acetylene as a feedstock. This demand is reported (34) as growing from 54,000 metric tons of acetylene in 1989 to a projected level of 88,000 metric tons in 1994. 

Aromatic Isocyanates. A variety of methods are described in the Hterature for the synthesis of aromatic isocyanates. Only the phosgenation of amines or amine salts is used on a commercial scale (5). Much process refinement has occurred to minimise the formation of disubstituted ureas arising by the reaction of the generated isocyanate with the amine starting material. A listing of the key commercially available isocyanates is presented in Table 1. 

Synthesis. The most important starting material for rhodium compounds is rhodium(III) chloride hydrate [20765-98-4], RhCl3 nH2 O. Other commercially available starting materials useful for laboratory-scale synthesis include [Rh2(0000113)4] [5503-41 -3], [Rh(NH3)201]0l2 [13820-95-6], [Rh20l2(0O)4] [32408-34-7], and [Rh20l2(cod)2] [12092-47-6]. 

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