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I came across this reaction, but I have no idea what reaction is this. Can anyone please tell me?

What will be the products?

My first guess is that a carbene will be formed which will attack on the alkene, but I don't know what to do after that.

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Diazomethane under the action of light or heat releases nitrogen leaving a neutral, divalent carbon species with a lone pair and an empty orbital called a carbene. This carbene then reacts with the double bond of alkene breaking it to form a cyclo- species. in your example, cis-2-butene will react with diazonmethane to form cis-1,2-dimethylcyclopropane with no detectable amount of the trans isomer.

However, do note that if the same reaction is carried out via a triplet carbene, generated via triplet sensitization, then a 1.3:1 mixture of trans to cis dimethylcyclopropane is observed. [3]

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Source

  1. https://www.masterorganicchemistry.com/2011/11/05/reagent-friday-diazomethane-ch2n2/ [Source for pic. 1]
  2. http://www.ochempal.org/index.php/alphabetical/c-d/diazomethane/ [Source for pic. 2]
  3. http://reag.paperplane.io/00000832.htm
  4. https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modules_(Organic_Chemistry)/Alkenes/Reactivity_of_Alkenes/Diazomethane%2C_Carbenes%2C_and_Cyclopropane_Synthesis
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