here is my solution (hopefully i haven't overseen something...):

#!/usr/bin/perl

use strict;
use warnings;

my @in = (1 .. 12);
my @out = reverse @in[$#in / 2 + 1 .. $#in];

splice @out, $_ * 2 - (($_ % 2) ? 1 : 2), 0, $_ for (@in[0 .. $#in / 2
+]);

print "in: \t@in\n";
print "out: \t@out\n";
[download]

prints:
in: 1 2 3 4 5 6 7 8 9 10 11 12
out: 12 1 2 11 10 3 4 9 8 5 6 7

bye

update 1: corrected the code and added the output