Check to be sure it was planted at the right depth and that there's no mulch up around the trunk. Otherwise, Jap maples don't like being wet, so I would only water when needed. Use your finger and see if the root ball is moist or not. If the top inch or so of soil is dry, then water. I would not rule out disease such as Verticillium wilt, however you will want to check with your Extension service to diagnose that.

If that was my tree I would be concerned about the direct sun until 11am. I live in so cal and that morning sun can get hot in the summer. I know it can burn leaves on my patio jmaples if they are high enough that they come through the patio cover.

Your best indicator is that the one branch in the shade looks good. I would not worry about the tree dying, just because the leaves are burnt. Maybe give it a year to adjust by growing deeper roots. It really needs to be watered deeply and let the surface dry out between waterings. This will encourage deeper roots. Jmaples are really meant to be under something, like a layer of taller trees, like an understory tree.

I don't think it is that unusual for Japanese maple leaves to suffer stress from the sun the first year of planting. There may be nothing wrong, just wait for the tree to get more established. The new leaves are often tender, and are the first to suffere from the sun. If the tree still has plenty of leaves on the tree, I would not worry.

I have a Full Moon 'Aureum' and some of the new growth leaves are the first to burn it seems, even thou the tree has been growing well for a couple of years.

Nailbird, You must live on the Western shore. Your sun exposure in the morning followed by shade in the afternoon is fine. Dont try and overcompensate for this heatwave by excessive watering, it wont do it. Providing your tree is not root bound and you 'teased or straightened' them if they were circling the pot they came out of, your tree is just being stressed from its new location and conditions. Dont water overhead like a sprinkler,dont fertilize and i wouldnt plant flowers or anything at all at the base of the tree that could interfere with its root system. Your tree is far from established and what you are experiencing is not uncommon.Your tree will acclimate and recover on its own with time.
regards AL