Due to their inherent ring strain and electrophilicity, epoxides are highly attractive building blocks for fundamental organic reactions. However, controlling the regioselectivity of disubstituted epoxide transformations is often particularly challenging. Most Lewis-acid mediated processes take advantage of intrinsic steric or electronic substrate bias to influence the site of nucleophilic attack. Therefore, the scope of these systems is frequently quite limited. Herein, we report two classes of epoxide carbonylation catalysts, which preferentially enhance or overcome substrate control to target different _-lactone regioisomers using 2,2-disubstituted starting materials. ,-Disubstituted _-lactones were obtained using traditional [(porphyrin)Al(THF)2][Co(CO)4] complexes, which increase the effects of intrinsic substrate bias. Mechanistic studies revealed epoxide ring-opening as the turnover limiting step, an insight that facilitated the improvement of reaction conditions using weakly donating, ethereal solvents, further increasing regioselectivity. Various epoxides were carbonylated to _-lactones, which were subsequently ring-opened to produce ketone-based aldol adducts, providing an alternative to the Mukaiyama aldol reaction. To specifically target the opposite lactone regioisomer, we developed a class of bulky sandwich-type catalysts. Contrary to systems which exploit inherent substrate- control, these sterically encumbered complexes install carbon monoxide at the substituted epoxide carbon with unprecedented regioselectivity. Further catalyst development and condition optimization improved catalyst lifetimes and solubility while suppressing side product formation. This new, catalyst-controlled process was used to target pivalolactone from isobutylene oxide and ultimately improve the economic feasibility of poly(pivalolactone) industrialization. Collectively, these two regioselective carbonylation studies demonstrate the power of innovative catalyst design to both utilize and oppose substrate-bias. Inspired by epoxide carbonylation reactions, which typically employ cobalt carbonyl anions, we explored the reactivity of [(ligand)Al(THF)2][Mn(CO)5] complexes with 2,3-disubstituted epoxides. Instead of generating _-lactone products, alkenes were observed, revealing a two-step epoxidation/deoxygenation process that results in overall inversion of alkene stereochemistry. Unlike most deoxygenation systems, which are typically stereoretentive, carbon monoxide was used as the terminal reductant, generating carbon dioxide as the only byproduct and preventing difficult postreaction separations. Various alkyl-substituted cis- and trans-epoxides were reduced to trans- and cis-alkenes, respectively, offering an alternative to direct, yet limited, alkene isomerization approaches.