Highcharts is not providing options for auto rotating data labels in pie chart. You can write your custom function for dataLabels rotation.
Here is simple example how you can do it:
var allY, angle1, angle2, angle3,
rotate = function () {
$.each(options.series, function (i, p) {
angle1 = 0;
angle2 = 0;
angle3 = 0;
allY = 0;
$.each(p.data, function (i, p) {
allY += p.y;
});
$.each(p.data, function (i, p) {
angle2 = angle1 + p.y * 360 / (allY);
angle3 = angle2 - p.y * 360 / (2 * allY);
p.dataLabels.rotation = -90 + angle3;
angle1 = angle2;
});
});
};
First I am calculating sum of all Y values. Then I am calculating the angle of middle of all pie slices. Then I am rotating data labels by the same angle.
example:
http://jsfiddle.net/izothep/j7as86gh/6/