DIazo transfer reaction onto γ‐butyrolactams (activated by α‐ethyloxalylation) gave rare α‐diazo γ‐butyrolactams. Decomposition of the latter by Rh2(OAc)4 in the presence of alcohols and water gave products of O–H insertion of the respective metal‐cabene species. Silver triflate (1 mol‐%) was found to convert the γ‐butyrolactams investigated into 1,5‐dihydro‐2H‐pyrrol‐2‐ones which represent versatile building blocks. Particular instability was noted for α‐diazo γ‐butyrolactams bearing alkyl or o‐substituted aryl substituents on the nitrogen atom. These were found to dimerize in solution or upon storage at room temperature to give fully conjugated bis‐hydrazones along with the loss of a nitrogen molecule.

Diazo transfer reactions are notoriously associated with the use of potentially explosive sulfonyl azides. Handling of the latter can be avoided with the use of this new protocol.

A convenient general approach towards 1,4-disubstituted αdiazo glutaconimides starting from β-substituted glutaconic acid anhydrides has been developed. It involves condensation with amines and subsequent diazo transfer reaction. This new class of diazocarbonyl heterocycles has been converted into a series of polysubstituted pyridine-2,6(1H,3H)-diones and oxazolo[5,4-b]pyridin-5(4H)-ones via a Rh 2 (esp) 2-catalyzed XH-insertion reaction and [3 + 2] cycloaddition with nitriles, respectively. Results and discussion Glutaconimides 5, precursors of the target diazo compounds 4, were obtained by analogy with the methods described in the literature [21] from synthetically available β-substituted glutaconic acid anhydrides 6. [18-19] Initial attempt at the Regitz diazo transfer using an equivalent amount of a base (DBU, TEA, DIPEA) resulted only in a negligible yield of 4. This was

Preparation of CH‐diazomethane sulfonamides has been developed for the first time. Their utility as a new type of diazo reagents was showcased in cycloaddition reactions with electron‐deficient alkynes and β‐nitro styrenes which delivered medicinally important pyrazole‐3‐sulfonamides in good to excellent yields.

Thermally promoted reaction of α-acyl-α-diazoacetates with imines has been investigated. The transformation, earlier reported predominantly under transition metal catalyzed conditions, delivers α-alkoxycarbonyl-substituted β-lactams with outstanding diastereoselectivity. DFT calculations performed in order to evaluate energetically feasible reaction pathways revealed the intermediacy of 1,3-oxazin-4-one intermediates hitherto never implicated in the Staudinger synthesis of β-lactams.