complicated dict comprehension

[rootVIII]

# Initial dictionary
d = {
    'one': 'some val',
    'two': 'some val',
    'three': {
        'subkey_1': 'some val',
        'subkey_2': 'some val'
        },
    'four': 'some val',
    'five': {
        'subkey_1': 'some val',
        'subkey_2': 'some val'
        },
    'six': 'some val'
}

# This results in the dictionary that I want:
new = {}
for k, v in d.items():
    if not isinstance(v, dict):
        new[k] = v
    else:
        for i, j in v.items():
            new['%s_%s' % (k, i)] = j
print(new)


# example correct output:
# {
#     'one': 'some val',
#     'two': 'some val',
#     'three_subkey_1': 'some val',
#     'three_subkey_2': 'some val',
#     'four': 'some val',
#     'five_subkey_1': 'some val',
#     'five_subkey_2': 'some val',
#     'six': 'some val'
# }


# But can this be done in a dict comprehension?
# I am trying this:

new = {k: v if not isinstance(v, dict) else {i['%s_%s' % (k, i)]: j for i, j in v.items()} for k, v in d.items()}
print(new)

# But I suspect that inner dictionary needs to be unpacked somehow? Is this possible? Maybe with another technique?