Described herein are three projects in the field of organic chemistry pertaining to the asymmetric synthesis of isochromans and isochroman-based natural products by C–H insertion reactions with donor/donor carbenes. The first chapter details the development of a methodology to stereoselectively synthesize isochromans. This work expands on our previous reports by accommodating six-membered ring substrates, notably with perfect diastereoselectivity in all cases and without observation of Stevens rearrangement byproducts. The second chapter employs this methodology towards the asymmetric total synthesis of panowamycin A, panowamycin B, TM-135, and veramycin F. The synthesis of the proposed structure of panowamycin A revealed a stereochemical misassignment. Computational NMR was used to predict the isomer most likely to be the natural substance; the synthesis of this compound was completed and the spectral data were consistent with the reported natural product, therefore confirming the structure to be correct. The third chapter involves the synthesis of tetrasubstituted geminal acyl/alkoxy allenes, which was incidentally discovered while exploring the substrate scope for isochroman formation. With support from byproduct identification and control experiments, the mechanism of formation for these novel compounds is proposed. This new class of allenes was then explored as a reagent in subsequent transformations, where they demonstrated unique reactivity.