Can not redirect https with upstream directive

With such config a I get redirecting to google.com

server {
    listen 80;

    proxy_ssl_server_name on;
    rewrite_log on;

    location / {
        proxy_pass https://google.com;
    }
}

but if I add upstream instead of host

upstream some-backend {
    server google.com:443;
}

server {
    listen 80;

    proxy_ssl_server_name on;
    rewrite_log on;

    location / {
        proxy_pass https://some-backend;
    }
}

I am getting error from google

It is because of fqdn. On the server is sent ip instead of fqdn. You can fix it with that config:

upstream google.com {
    server 10.16.1.51:443;
}

...
proxy_pass https://google.com;
proxy_ssl_server_name on;

or you can manually set headers in location section:

location / {
    proxy_pass https://some-backend;
    proxy_ssl_server_name on;
    proxy_ssl_name google.com;
    proxy_set_header Host google.com;
}