Alternative Synthetic Strategies

An alternative synthetic strategy for sulfur-nitrogen oxides is exemplified by the more recent reaction ... 

Sathish M, Viswanathan B, Viwanath RP (2006) Alternate synthetic strategy for the preparation of CdS nanoparticles and its exploitation for water splitting. Int J Hydrogen Energy 31 891-898... 

Polysilanes with functionalities Z directly attached to the silicon main chain are generally more difficult to synthesize and less stable, due to the reactivity of both the Si-Z and Si-Si linkages. Such polymers are usually not accessible via the Wurtz-type coupling reaction, and alternative synthetic strategies (see Sections 3.11.4.1 and subsequent) or postpolymerization techniques have to be employed. 

Reductive ring closure of l-(2-nitrobenzyl)-2-pyrrole carbaldehyde 200 results in pyrrolo[2,l-c][l,4]benzodiazepine 201 (Scheme 42 (1999BMCL1737)). On the other hand, oxo derivative 203 can be synthesized starting from aldehyde 200 through a nitrile formation/cyclizations multistep sequence. The alternate synthetic strategy included reduction of the intermediate acid (R = H) or ester (R = Et) 205 followed by CDI or thermal cyclization (1992JHC1005). 

An alternate synthetic strategy for benzodiazepines involves the condensation of resin-bound a-amino esters 17 with 2-aminobenzophenone imines followed by TFA treatment of the intermediate to effect cleavage and cyclization [27], The parallel synthesis of 40 discrete benzodiazepine analogs 18 was performed, and expected SAR data were generated in a bioassay based on the inhibition of fluoronitrazepam (Fig. 4). 

The search for halocarbenes led to Fischer s carbyne synthesis (see below) however, such halocarbene complexes are now widely available for elements of Group 6-9, albeit via alternative synthetic strategies. The first stable example arose from a study of the biochemically relevant reactions... 

Therefore we have dedded to follow an alternative synthetic strategy for the ftmctionalisation of hydroxyls at C-3 and at C-4. Scheme S reports the passed methodology. 

An alternative synthetic strategy for eletriptan (20, R = PhSO2CH=CH) is reported... 

It is particularly difficult to carry out a ring opening in compounds containing the oxabicyclo[2.2.1] nucleus without concomitant aromatization, because the strong acidic conditions can also lead to dehydration. On the other hand, inducing aromatization under controlled conditions permits the synthesis of highly-substituted aryl compounds as an alternative synthetic strategy to traditional electrophilic aromatic substitution . The methods to aromatize oxabicyclo [2.2.1 ] heptanyl derivatives by the use of acids and low valent metals have been reviewed [172]. 

The discovery of l-thioniabicyclo[4.4.0]decane (TBD) tetrafluoroborate (I) dates back to Eastman s synthesis in 1959 <59JOCi428>. The bicyclic bridgehead sulfonium salt is consequently referred to as Eastman s sulfonium salt <77JA2337>. Heathcock and co-workers subsequently developed alternative synthetic strategies allowing the functionalization of each ring <79JA2971>. 1-... 

An alternative synthetic strategy was used involving the use of a masked diene as a sulfolene intermediate that, when heated, undergoes tandem chelotropic SO2 extrusion followed by a Diels-Alder cyclization (Scheme 20). The final result is the construction of a C-5 epimer of the... 

The coupling reactions discussed so far in this Section involve a m-terphenyl base and a prefabricated vault, and revealed a propensity for the formation of self-filled over vaulted conformers. The alternate synthetic strategy, to attach a... 

Synthesis of repaglinide involves condensation of an appropriately substituted and chi-rally pure benzylamine derivative with an appropriately substituted phenylacetic acid derivative (7) followed by saponification. The reported process for the key intermediate (7) described a five-step process with an overall yield of about 30% of theory (Scheme 23.4) We undertook development of an alternative synthetic strategy to prepare 7 and developed an efficient and commercially feasible synthesis starting from 2-hydroxy-4-methylbenzoic acid (9) in two steps. Thus, 9 was first alkylated with ethyl bromide in a polar aprotic solvent and in the presence of an inorganic base to afford ethyl 2-ethoxy-4-methylbenzoate... 

Scheme 80. Alternative synthetic strategies for the formation of heterobimetallic thioaroyl complexes.

Although radioiodinated antibodies have acceptable stability for in vitro applications, their in vivo stability is less ideal These tracers can act as substrates for the iodotransferase enzymes which are normally responsible for metabo lism of the thyroid hormones thyroxine and tri-iodothyronine which bear structural similarities. Although not present in the vascular circulation, these enzymes are widely distributed in many tissues and their action results in the intracellular release of the radionuclide which then either diffuses or is actively transported out of the cell and subsequently excreted in the urine. In order to try and increase the in vivo stability of antibodies labelled with radioiodine, alternative synthetic strategies have been pursued which result in molecules which are not substrates for the iodotransferases (11. 12). AU of these techniques are more complicated than the electrophilic substitution methods described above and require some synthetic chemistry in order to prepare the precursors which are not commercially available. 

---