Photochemical and thermal 1,2- and 1,4-cycloaddition reactions of azodicarbonyl compounds with monoolefins

Abstract

Dialkyl azodiformates form dihydrooxadiazines with indene, dihydro-1,4-dioxine, vinylene carbonate, cisand irons-1,2-dimethoxyethylene, and vinyl acetate by 1,4 addition; 1,2 addition yielding diazetidines is observed with vinyl ethers. Diazetidines also result from the addition of 4-phenyl-A'-1,2,4-triazoline-3,5-dione (PTD) to indene and dihydro-1,4-dioxine. Dihydrooxadiazines are formed in a concerted Diels-Alder reaction with inverse electron demand, the diazetidines via dipolar intermediates. The acceleration of azodiformate addition by illumination is due to the photochemical production of as azodiformates, which show increased thermal reaction rates compared with the irons isomers.

Recent trends in the synthesis of O-glycosides of 2-amino-2-deoxysugars

“…83 Herein, the application of the cycloaddition chemistry to the synthesis of 2-amino-2-deoxyglycosides is discussed. [84][85][86][87][88][89] Based on the published mechanistic studies of this reaction with simple substrates, Leblanc and co-workers reasoned that the diastereoselectivity of the cycloadducts would be most readily attainable with a rigid substrate having an appropriately placed substituent-for example, allylsubstituted cyclic vinyl ethers. 90 Since glycals fit this criterion, Leblanc et al explored the possibility of applying this reaction to the synthesis of 2-aminosugars from glycals.…”

Mechanistic Studies in Triazolinedione Ene Reactions

“…The slightly inverse KIE (k H /k D = 0.98 ± 0.02) clearly rules out the possibility that allylic hydrogen abstraction occurs in a slow step, compared to the preceding transition state of AI formation. If we consider formation of AI in the rate-limiting step, significant inverse a-and b-secondary KIEs would be expected 19 essentially due to the rehybridization of the olefinic carbons from sp 2 to sp 3 . It seems that in the addition of PTAD to 61-d 0 , the transition states of the two reaction steps are close in energy, with formation of AI probably being slightly higher.…”

“…20 In that study we explored the diastereoselectivity of the ene reaction of MTAD with allylic alcohol 63-d 0 . For this reason, we also used its deuterated analogs 63-d 9 , 63Z-d 3 , and 63E-d 3 (Scheme 14).…”

Solvent‐Dependent Changes in the Triazolinedione–Alkene Ene Reaction Mechanism

“…Among these, the formation of a closed, three-membered aziridinium imide (AI) intermediate ( Figure 1) was the most popular, and initially found support in the results of trapping experiments. [11,12] Subsequently, isotope effect measurements on deuterium-labeled tetramethylethylenes (TMEs) [3,4] and 2-butenes [5,6] also suggested the formation of an AI intermediate in the rate-determining step of the reaction. Thus, large intramolecular kinetic isotope effects (KIEs) were found in the ene reactions of RTADs with the cis-related methyl and deuteriomethyl groups in substrates 1 and 2 (H/D isotopic competition; Scheme 1), whereas only a small isotope effect was observed with the trans-related groups in compound 3 (no isotopic competition).…”