Test.tex

\documentclass[english,
10pt,
]{scrreprt}

\usepackage{chemmacros}
\usechemmodule{
	spectroscopy,
	scheme,
	nomenclature,
	mechanisms,
	isotopes,
}

\setchemnum{
	replace-tag={X},%X<#> used as template tag, better visualization in chemdraw file than TMP<#>
	show-keys=ref,
}

\usepackage[runs=2]{auto-pst-pdf}

\begin{document}

Here the numbers are defined: \cmpd{Garner_02} and \cmpd{Garner_04}

\begin{scheme}[htb]
	\centering
	\replacecmpd{Boc-ser-OMe}
	\replacecmpd+{Garner_02}
	\replacecmpd+{Garner_04}
	\replacecmpd{Garner_22}
	\includegraphics[scale=0.7]{garner_rxn}
	\caption{Synthesis of Garner's aldehyde~\cmpd+{Garner_04} and the corresponding Weinrebamide~\cmpd+{Garner_22}.}
\end{scheme}

Here they are referenced: \cmpd{Garner_02} and \cmpd{Garner_04}

\end{document}