Borsche synthesis

Boroxazothienopyridines, 4, 1029-1032 Borsche synthesis, 3, 44 Botrydiplodin mass spectrometry, 4, 585 Boulton-Katritzky rearrangement, 5, 288 Bovine milk xanthine oxidase substrates, 1, 234 Bradsher reaction... 

A large rtumber of carbazole syntheses involve the preparation and dehydrogenation of hydrocarbazoles, mainly 1,2,3,4-tetrahydrocarbazoles. They are usually prepared by either the Fischer-Borsche synthesis or the Japp-Klingemann reaction. The most commonly used dehydrogenating agents are palladium on charcoal or chloranil (495,496). 

The Borsche synthesis of tetrahydrocarbazoles 21 is a special case of the Fischer indole synthesis in which cyclohexanone phenylhydrazones 20 are used as the starting materials (Scheme 9) (see, e.g., <2009BML4110>). 

Quinolines from isatins Pfitzinger-Borsche synthesis... 

The tautomerism of the 4-cinnolone products of the Borsche synthesis has also been studied in detail. Studies have been carried out using infrared spectroscopy, ultraviolet spectroscopy, and more recently by NMR spectroscopy. All of these studies have shown that 4-cinnolones exist predominantly or exclusively as the 4-ciimolone tautomers in the solid state and in solution. 

A modification of the Borsche synthesis was disclosed in 1986, in which triphenylphosphoranylidene ketones 1 are diazotized to provide triphenylphosphorylidene cinnolones 2. Cleavage of the triphenyl-phosphorane with aqueous alkali affords the 4-cinnolone product 3. ... 

For example, the cinnoline 8 was synthesized for evaluation as an inhibitor of the twosine kinase domain of the epidermal growth factor receptor (EGFR). This was prepared from l//-4-cinnolone 6 by chlorination and subsequent displacement of chlorine by 3-bromoaniline, as shown in the previous page. The l//-4-cinnolone 6 was prepared in turn from (2-amino)acetophenone by the Borsche synthesis. 

Similarly, cinnoline inhibitors of the tyrosine kinase of the vascular endothelial growth factor receptor (VEGF), such as 10, have also been described. Again, the Borsche synthesis was used to construct the appropriately functionalized l//-4-cinnolone 9, which was then further elaborated to afford 10. ... 

More recently, a cinnoline containing inhibitor of protein kinase B (13) has been prepared through the use of the Borsche cinnoline synthesis. The origin of this product in the Borsche synthesis may not be immediately apparent, because there is no functional group at the 4-position of the cinnoline. In this case, the l/f-4-cinnolone product 11 of the Borsche synthesis was reduced to afford the desired intermediate 6-bromocinnoline 12, which was subjected to a Stille coupling to afford 13. 

In each of these compounds, the final targets shown were derived from l//-4-cinnolones prepared by the Borsch synthesis. For example, 14 was prepared ft om l//-4-cinnolone by iodination, JV-alkylation, and Sonogashira coupling as shown below. 

A review of cinnolines with biological activity, not limited to those prepared by the Borsche synthesis, has been published recently. ... 

Bischler-Napieralski synthesis (isoquinoline) 413 Bltimlein-Lewy synthesis (oxazole) 172 B oekelheide reaction 362 Bonnemann synthesis (pyridine) 373 Bohlmann-Rahtz synthesis (pyridine) 369 Borsche synthesis (cinnoline) 494 von Braun degradation 432 Brederek synthesis... 

Bechamp method, 129 Beckmann rearrangement, 94, 279 Benzilic acid rearrangement, 67-68 Benzoin condensation, 30 Bogoslovskii Reaction, 244 Boord synthesis, 17 Borsche synthesis, 244... 

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