It would likely depend upon the situation if you could obtain insurance or not. If you are buying a car so do not yet have the title because you have not yet taken possession of the vehicle then you can inform your insurance agent that you are in the process of buying a car to see if your current insurance coverage will cover this vehicle until you have the title or if they can place the car on the policy so that drive it away after purchasing it. You will normally need to give the insurance carrier more information on the vehicle after you have taken possession of the car in a case like this.
Another situation may be that you have inherited a car. In this type of situation yes, you can usually get insurance on the vehicle without the title, but you will have to show proof of ownership within 15-30 days to the insurance provider. That means that you would be getting the title and you would be registering the vehicle in your name within this time frame.
If instead you will not receive the title (pink slip) for awhile, due to some type of situation such as you are buying the car from a friend or relative in payments and they are keeping the title until you pay them completely for the vehicle then you may be able to find insurance but it will be more difficult since you do not have insurable interest in the vehicle.
Esurance is one company that in certain states does allow a person to insure a car even if they do not have insurable interest in it. This type of policy is sometime regulated by the state and other times by individual insurance companies if the state has no law or precedence.