We studied the stericcourse of aldol additions of CpTiCl2 (novel) or Bu2B enolates of the unsubstituted δ-lactone and of the four monomethylated δ-lactones to isobutyraldehyde, crotonaldehyde, and para-bromobenzaldehyde. The titanium enolates reacted syn-selectively with >95:5 ds in most cases. The boron enolates reacted anti-selectively without exception (ds = 98:2 to 92:8). These selectivities paired