>perl -wMstrict -le
"my @first_sentence = qw{ i am 2 ( but ) . };
 printf qq{'$_'  } for @first_sentence;
 print '';
 ;;
 my $ns = qr{ [().] }xms;
 ;;
 my $sentence = join q{ }, @first_sentence;
 print qq{'$sentence'};
 ;;
 $sentence =~ s{ [ ] (?= $ns) | (?<= $ns) [ ] }''xmsg;
 print qq{'$sentence'};
 ;;
 ;;
 use List::Util qw(reduce);
 ;;
 $sentence = '';
 $sentence =
   reduce { ($a =~ $ns || $b =~ $ns) ? qq{$a$b} : qq{$a $b} }
   @first_sentence
   ;
 print qq{'$sentence'}
"
'i'  'am'  '2'  '('  'but'  ')'  '.'
'i am 2 ( but ) .'
'i am 2(but).'
'i am 2(but).'