Bitcoin Core 0.17 sethdseed then dumpwallet how to recompute extended private masterkey?
Bitcoin Core uses the method described in BIP 32 to generate the master private key from a seed. The seed here is WIF private key. To get the master private key from the seed, you will need to decode the WIF private key to get the byte sequence that it represents. Then you can hash it as described in BIP 32 and encode it to get the master private key.

You can use bx to do this:

bx wif-to-ec &lt;WIF key&gt; | bx hd-new