Metal-stabilized carbenes derived from diazo compounds have become broadly useful reactive intermediates for organic synthesis. This tutorial review will describe the recent advances in using N-sulfonyl-1,2,3-triazoles as precursors for the formation of metal-bound imino carbene intermediates. These intermediates undergo a variety of synthetically useful transformations, which include transannulation reactions to generate new heterocycles, cyclopropanation and subsequent ring expansions, ylide formation with subsequent rearrangements, and C-H functionalization. Furthermore, many of these transformations can be conducted with high levels of enantioselectivity by use of chiral rhodium(II) catalysts.

Warming of 4-phthalimido-N-mesyl-1,2,3-triazole in the presence of alkenes followed by silica gel induced hydrolysis results in a highly diastereoselective and catalyst-free entry to N-phthalimidocyclopropanecarboxaldehydes.

Catalytic enantioselective methods for the generation of cyclopropanes has been of longstanding pharmaceutical interest. Chiral dirhodium(II) catalysts prove to be an effective means for the generation of diverse cyclopropane libraries. Rh2(R-DOSP)4 is generaally the most effective catalyst for asymmetric intermolecular cyclopropanation of methyl aryldiazoacetates with styrene. Rh2(S-PTAD)4 provides high levels of enantioinduction with ortho-substituted aryldiazoacetates. The less-established Rh2(R-BNP)4 plays a complementary role to Rh2(R-DOSP)4 and Rh2(S-PTAD)4 in catalyzing highly enantioselective cyclopropanation of 3- methoxy-substituted aryldiazoacetates. Substitution on the styrene has only moderate influence on the asymmetric induction of the cyclopropanation.

Highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) tuning is an important consideration in the development of organic-based semiconducting materials. A study of the specific effects and overall trends for the HOMO-LUMO tuning of a diverse series of 9-fluorenones by means of extended conjugation and substituent effects is described. Trends were explored in a range of compounds, beginning with structures having highly electron-withdrawing substituents and progressing to structures having highly electron-donating substituents. Compounds with an incremental increase in conjugation were also examined. Electrochemical and optical measurements were used to calculate the HOMO-LUMO levels and HOMO-LUMO bandgap (HLG) for each structure. Results from both methods were compared and correlated with the differences in molecular structure. Increasing the electron-donating character of the substituents was observed to decrease the HLG and increase the energy levels of the HOMO and the LUMO, whereas an increase in the electron-withdrawing character produced the opposite results. Increasing conjugation decreased the HLG, increased the HOMO energy level, but decreased the LUMO energy level. Spectroscopic evidence of substituent influence on the carbonyl suggests that substituents directly impact the HLG by influencing the availability of nonbonding electrons within the carbonyl, which impacts the probability of an nπ* transition. The data presented not only elaborate on the HOMO -LUMO tuning of 9-fluorenone systems but also enable the consideration of 9-fluorenones as analogous models for HOMO-LUMO tuning in other more complex polyaromatic systems such as bifluorenylidenes. These trends may provide insight into developing materials with specifically tuned HLGs and HOMO-LUMO levels for a variety of applications.

A highly effective synthesis of 2,3-fused pyrroles from cyclic ketones has been achieved. The transformation includes a rhodium-catalyzed reaction of 4-alkenyl-1-sulfonyl-1,2,3-triazoles featuring an unusual 4π electrocyclization. The methodology was further extended to the synthesis of indoles using a one-pot reaction starting from 1-ethynylcyclohexenes.