A mixture of t-butylzinc halide and an aldehyde reacts with conjugated dienes to provide 2-neopentyl homoallyl alcohols in high yields by 1,2-addition. Without the aldehyde, under carbon dioxide atmospheric pressure, the three components of t-butylzinc halide, butadiene, and carbon dioxide combine in a 1 : 1 : 1 ratio to give 2-neopentyl-3-butenoic acid in excellent yield.