[Zalzul]

In performing ozonolysis on , specifically with the procedure of (step 1) O₃ @ -78 °C and (step 2) (CH₃)₂S in water, I came up with 3 different products:

, , and

Given the subsequent reaction (reduction with sodium borohydride in methanol followed by acidic workup), I was confused as to the point of trying to generate multiple products: methanol, glycolic acid, and acetic acid.  According to the book, the only product to consider is the middle one: , with the end product (following the aforementioned reduction and subsequent treatment with hot sulfuric acid) being prop-2-enoic acid.  This acid then goes on to be the dienophile in a Diels-Alder reaction.

In reflecting on this, I cannot reason as to why one would discount the methanol and acetic acid, for fear of unwanted ether and/or ester products given the hot and acidic environment once the sulfuric acid is added.

Can someone clarify for me as to why I needn't consider either formaldehyde or acetic acid in the ozonolysis of pent-1-en-4-yne?  Thanks in advance.

[Mitch]

I think the trick is to stop it from letting the reaction go all the way to completion. It should react with the triple bond first and more often than not.

[Zalzul]

Ah, I see; perhaps then that's what meant by the cold temperature during the ozonolysis step.

[Mitch]

That's what caught my eye as well.