Since your capture groups define explicitly one character on either side of the common word, it's looking for space
word
space
and then when it doesn't find another space
, it fails.
In this case, since you don't want to match all the characters word boundary's would catch (period, apostrophe, etc.) you need to use a bit of trickery with lookaheads, lookbehinds, and non-capture groups. Try this:
(?:^|(?<= ))(one|common|word|or|another)(?:(?= )|$)
Word boundaries are still simpler to implement, so for reference sake, you could also do this (though it would include '
, .
, etc.).
\b(one|common|word|or|another)\b