How can the following compounds be prepared using ethyne as...

Key Concepts

Alkyne Reactivity

The reactivity of alkynes is centered on their highly unsaturated carbon?carbon triple bonds. These bonds are electron rich and can undergo electrophilic addition reactions. Their unique linear geometry and bond strength influence the outcomes—both in terms of regiochemistry and stereochemistry—when using specific reagents and conditions to construct a variety of useful functional groups.

Acetylide Ion Formation

Terminal alkynes, such as ethyne, possess an acidic hydrogen that can be abstracted using strong bases to form acetylide ions. These ions are powerful nucleophiles which can attack electrophilic centers to forge new carbon–carbon bonds. This transformation is crucial in synthesis, allowing the construction of more complex molecular frameworks from simple alkyne starting materials.

Electrophilic Addition Reactions

Electrophilic addition reactions to alkynes are fundamental in transforming the triple bond into more reactive double bonds or fully saturated systems. Under controlled conditions, reagents such as halogens, acids, or water add across the triple bond, and the reaction may be tuned to favor specific products by controlling the reaction conditions and catalysts, leading to either dihalo, hydrohalogenated, or hydrated products.

Hydration Reactions

Hydration reactions involve adding water across the alkyne's triple bond, typically in the presence of acid catalysts or mercuric salts. These conditions lead initially to an enol intermediate which rapidly tautomerizes to a carbonyl compound. This approach is widely used to synthesize aldehydes or ketones from alkynes, offering control over regioselectivity and functional group placement.

Transcript

00:06 This question asks how all of these compounds can be prepared using affine as the starting material.

00:12 So this is what affine looks like.

00:14 It's also called acetylene in the common name.

00:18 So to make a, it's actually just a one step synthesis here.

00:25 We're going to do acetyacetalized hydration with the help of the mercuric ion because it's a terminal alkyne.

00:31 So we'll have huso4, water, and the mercuric.

00:37 Like ion and that will give us an enol at first that will look like this and then that will atomize into our product from part b we can see that we've got some more going on here so the first thing i like to look at is where that triple bond was from the fion so it can be either here or here it's symmetrical so it doesn't matter so what we do know is that if we put it in there we have to add carbons to each side so the way that we do that we start with our a thine is we first use sodium amid to take off that hydrogen and then we use a halo alkan to add on a carbon chain so we'll use ch3 br to do this side over here so then we'll get ch3 on one side and then we need two carbons on the other side so we'll do that again n -h2, and then this time we'll use ethobromide.

01:41 You can use ephylacloride.

01:42 Either one is fine.

01:43 And then we'll get our ephil group on that side.

01:51 And then to get from an alkyne to an alkan with a bromine, the first thing we're going to have to do is reduce it to an alken.

02:00 So you can either do h2 with the lindlar catalyst here, or you can do sodium and liquid ammonia.

02:09 Either one is fine, and that will give us an alken.

02:17 And then to get from an alken to an alkene to an alkali bromide, we're going to add one equivalent of hbr.

02:27 For c, again, we have to add one carbon on here...