If you are a Singapore citizen and legally married to your spouse, they can apply for PR. Getting PR for the spouse of a Singapore citizen is not much difficult. According to the Ministry of Home Affairs, the success rate in this scenario is 49%, much better than applying for PR under other schemes.
However please note approvals under this scheme are not fast. We think Ministry is worried about sham marriages being done for PR / Citizenship. So typical approach is to wait for few years and see the status of marriage before approving the PR.
So do not expect to get approval under this scheme fast.