Iodenium or Phosphonium: The Ambi-Valent Character of Iodophosphonium Complexes.

The ambi-valent character of the P-I bond in iodophosphonium complexes ensures that it can be electrophilic at either P or I. Herein, we use an ensemble of computational tools and methodologies to probe the nature of this ambi-valent bond. Geometric and atomic electron population analyses yielded strong trends between the electron donating ability of the phosphine and the strength and polarity of the P-I bond. Quasi-atomic orbital analysis demonstrated the near homo-polarity of the P-I bond, and energy decomposition analysis calculations demonstrated the ability to tune the polarization of the bond with only mild changes in secondary structural features. Finally, the ambi-valent nature of the P-I bond was demonstrated to follow hard-soft considerations in reactions with nucleophiles, with harder nucleophiles preferentially forming products of addition to P and softer nucleophiles to I.

Borane- and Silylium-Catalyzed Difunctionalization of Carbohydrates: 3,6-Anhydrosugar Enabled 1,6-Site Selectivity.

A novel diastereoselective, Lewis acid catalyzed 1,6-difunctionalization of galactose and mannose derivatives has been developed in one pot, via sequential nucleophile additions. Our studies point to the formation of a 3,6-anhydrosugar intermediate as key to the 1,6-site-selectivity. Starting material-specific reactivity occurs when competitive ring-opening C-O cleavage is possible, owed to basicity and stereoelectronic stabilization differences. Lastly, Mayr nucleophilicity parameter values helped predict which reaction conditions would be most suitable for specific nucleophiles.