Question

Write a short account on the chemical and IR spectroscopic evidence for the existence of benzyne.

Despite the expense and time commitment, the total synthesis of large natural products continues to be of great use. Give two reasons why.

Answer 1

Benzyne , is a reactive intermediate. It's presence has been established by chemical and spectroscopic means. Benzyne (C₆H₄) can be trapped in chemical reaction as it readily undergoes 2+4 cycloaddition reaction (diels alder reaction), it has been trapped using anthracine, furane and butadiene as it gives 2+4 adduct :

Similarly, 14-C studies of Elimination-Addition Mechanism of Nucleophilic Aromatic Substitution of Haloarenes also give evidence for existence of it.

IR : Low temperature IR for reaction medium having benzyne as intermediate gave ~2000-2100 cm-1 band which corresponds to triple bond , thus suggesting Benzyne existence. It occurred in addition to other bands for aromatic benzene system.

2. Despite the expense and time commitment, the total synthesis of large natural products continues to be of great use :

Total synthesis of Natural products is really a daunting task, as it involves multiple steps and separations ,stereocontrol. A natural product might have many chiral centres , thus so many stereoisomers, synthesising biosimilar / bio-equivalent product requires lot of expenses and commitment . But, it have great importance :

• As natural products continue to provide diverse and unique source of bioactive molecules for drug discovery , antioxidants , flavours etc. but meeting demands from natural sources is difficult with overexploitation of biological diversity. Total synthesis of NP is alternative way to it.
• It make availability of bioactive compounds easier and cheaper, thus better coverage.