Thank you for contacting Ask Extension. Since I do not see any insects or diseased leaves, it is difficult to determine what is wrong with your Rose of Sharon. But you can determine if the branches are healthy, by lightly scratching them about 1/2 way down to see if there is any green underneath the bark. If there is then the plants could have had winter injury and the leaves just fell off. If it is not green, then the branch is dead (possibly from winter injury) and you can prune down to where you see any green. The part that I see that is growing looks healthy. 

It appears to be in need of pruning to thin it out. You would cut down to the crown of the plant about 1 out of every 3 branches. That way, you can also determine if they are healthy if you see any green under the bark. You should only take about 5-6 stems from this plant. Prune out any crossing branches, and then I would leave the rest until fall to cut. 

If it is indeed winter injury, the shrub still can come out of it. This year was a hard winter for many shrubs. So by letting it 'sit' until fall, you might begin to see some growth, if the branches are still live. 

If you need to prune this fall, because the branches are dead, understand that you are possibly cutting next year's flowers off. But sometimes you need to do that. 

I am including some references about the Rose of Sharon and also pruning instructions. 

https://plants.ces.ncsu.edu/plants/hibiscus-syriacus/

https://www.thespruce.com/when-to-prune-rose-of-sharon-8712662

https://extension.umn.edu/planting-and-growing-guides/pruning-trees-and-shrubs

https://hort.extension.wisc.edu/articles/pruning-deciduous-shrubs/

If we can be of further help, contact us.

Thank you Diane!  You’ve been a tremendous help, as always. Sandy

You are welcome! Good luck!