How to draw resulting products from given reactions, as well as providing accurate stereochemistry and regiochemistry

Question

How could I work out and what would be the resulting products (major and minor in some cases) from the given reactions in the following image https://ibb.co/w06DKxS

Also, where applicable, how can I simply work out their accurate stereochemistry and regeochemistry?

Answer 1

You first need to memorize what each reagent does in general, your text should have a summary of each reagent in each chapter. Most of the time, in these kinds of problems, you only need to recognize the first step; the second step is almost always linked to the first one. For example, OsO4 always does the same thing: it adds -OH to each carbon of an alkene. The second NaHSO3 step is just a way to remove the Os from the reaction intermediate - that strategy cuts down on the material you need to memorize.

A general trick that can help you predict products is to recognize oxidizing agents, reducing agents, nucleophiles, and electrophiles. Going back to OsO4, you've got a reagent that's loaded with oxygen. It's usually a safe bet that some of those oxygens are going to end up on your product. Similarly, if you see a bunch of hydrogens attached to not-so-electronegative atoms like Li, B, or Al, you can bet those hydrogen(s) will end up on your product in a reduction. So even if you forget the specifics, you can probably expect partial credit if you give a reasonable oxidation/reduction/addition product as appropriate to the reagent.

As far as regio/stereochemistry goes, your text usually floods you with information by providing a mechanism to explain the observed regio/stereochemistry. Not all instructors require you to memorize the mechanism, but it can be helpful to know what intermediates are formed in order to predict the products. Do you form a carbocation? That'll be on the most substituted or resonance-stabilized position. Is there a ring formed in the intermediates? The added groups will likely be Syn; and so on. Memorizing this kind of information will help you answer deeper questions or questions that require an explanation.