I am studying for the International Chemistry Olympiad and some of questions involve synthesis of complicated organic compounds and i have no idea how to do them.

The setting of the questions is usually like this: they give you a rough idea of the end product however some of the groups are replaced with R. They replace all the other intermediates with A, B, C ... They also give the reactants and catalysts for each step.

Most of the time the catalysts are lewis acids. I wondering if you were able to provide mechanisms and general resulting reactions of these catalyses so i could predict what the product will be.

Also, is $\ce{NaBH4}$ a lewis acid?

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    $\begingroup$ Welcome to chemistry.se! I am afraid, I do not quite understand what you are asking. I might be better, if you could provide us with a specific question, an example of what you are struggling with. In its current form, this question might be too broad and is likely to be closed. You also might want to consider to ask two separate questions for the two problems you face. $\endgroup$ – Martin - マーチン Jan 5 '15 at 8:17
  • $\begingroup$ Ask yourself: can NaBH4 accept anymore electrons? Remember the octet rule. $\endgroup$ – Jori Jan 5 '15 at 8:28
  • $\begingroup$ Can you provide a specific example of a question, so we know the exact context? $\endgroup$ – John Snow Jan 5 '15 at 8:53
  • $\begingroup$ Hi, thanks for reading my question and sorry for being really confusing. I cant write the question down as it is really long and i cant draw the structures here. Here is the link to the question- file:///C:/Users/pc/Downloads/volume3-icho41-45.pdf $\endgroup$ – user11603 Jan 5 '15 at 9:08
  • $\begingroup$ It is the 7th question from the 2011 paper on page 1272. $\endgroup$ – user11603 Jan 5 '15 at 9:08

Firstly, $\ce{NaBH4}$ is not a Lewis acid because it cannot accept any more electrons. Aqueous $\ce{NaBH4}$ is a commonly used reducing agent often for reduction of carbonyls to their respective alcohols.

The mechanism of Lewis acid catalysis depends on the reaction but often Lewis acids are used to generate cationic electrophiles such as in the Friedel-Crafts reaction. enter image description here

  • $\begingroup$ Thank you for answering my question. However is there any other reaction mechanisms involving lewis acid catalysts? $\endgroup$ – user11603 Jan 5 '15 at 10:08
  • $\begingroup$ @the any reaction where you want a cationic electrophile could quite easily involve a lewis acid. are you thinking of any specific example? $\endgroup$ – bon Jan 5 '15 at 18:08