59). Diazocarboxylate esters (61) undergo photochemically induced cy~loaddition'~ with glycals (60) to give adducts (62) which are powerful glycosylating reagents and which can be reduced to 2-aminoglycosides (63) (Scheme 9).96Reagents: i, hv (350nm), cyclohexane; ii, R'OH; iii, Raney Ni, H2 Scheme 93 Functional Group Manipulation Addition Reactions.-The Cieplak theory has stimulated several groups to investigate additions to ketones and alkenes with 'remote' substituents. Electron-withdrawing equatorial substituents at the 3-position of cyclohexanones and methylenecyclohexanes clearly favour axial attack in a wide range of addition reaction^,^' but the results are much less clear-cut for substituents at the 2-po~ition.'~ Epoxides.-The Sharpless asymmetric epoxidation reaction continues to find new application^,^^-'^' but no ligands superior to tartrate esters have been found.lo2 Useful stereoselectivity can be achieved with other transition-metal catalyst^;'^^ for example, epoxidation of norbornene by Cr"' porphyrins is highly selective for the ex0 face.'04

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