Azure ARM template - using array variable

I am defining an alertrule inside my template.json with custom eMails which shall be alerted in case of an error. So the JSON snippet looks like this:

"resources": [
    {
        "type": "microsoft.insights/alertrules",
        "properties": {
            "action": {
                "customEmails": [
                    "user01@contoso.com",
                    "user02@contoso.com"
                ]
            }
        }
    }
]

Now I'd like to store these emails as an array-variable, something like this:

"variables": {
    "alertEmails": [
        "user01@contoso.com",
        "user02@contoso.com"
    ]
},
"resources": [
    {
        "type": "microsoft.insights/alertrules",
        "properties": {
            "action": {
                "customEmails": "[variables('alertEmails')]"
            }
        }
    }
]

This doesn't work, but I didn't found out what the correct syntax is. Can someone tell me?