Diazirines 3,3-dialkyl

The absolute rate constants for oxygen and sulfur transfer to a range of carbenes (dialkyl, cycloalkylidene, alkylchloro, diaryl, arylchloro, arylalkoxy, and dialkoxy), generated by laser flash photolysis of diazirine or oxadiazoline precursors, were determined. No evidence was seen for ylide formation and a concerted mechanism via an ylide-like transition state was proposed. 

Bicyclopropylidene (1) reacts with dimethoxycarbene generated thermally from the diazirine at 25 °C to give a complex mixture of products [116b]. The cycloaddition of several dialkoxycarbenes generated in situ from the corresponding 2,2-dialkoxy-A -l,3,4-oxadiazolines of type 134 with bicyclopropylidene (1) affords the dialkyl acetals of dispiro[2.0.2. l]heptanone 135 (Scheme 29 ) [1251. 

Photolysis of dialkyl- and alkyl-diazirines has been broadly investigated since the products formed gave evidence of shortlived intermediates possessing excess vibrational energy. As shown in Scheme 1 diazirines (3) were photoactivated to (235) by irradiation with a medium pressure mercury lamp with quantum yields smaller than one this means reversibly. Nitrogen extrusion yielded carbenes (236). These rearranged to the primary products, alkenes and... 

In contrast to 3-H-3-aryldiazirines, adamantane diazirine may be prepared in high yield by a method (Isaev et al., 1973 Bayley and Knowles, 1980) based on a general procedure for dialkyl diazirines devised by Schmitz and Ohme (1961) (Fig. 3.23). Such a convenient synthesis is most attractive but as yet adamantane diazirines further functionalized to allow their attachment to molecules of biological interest, have not been prepared, although this should not be a difficult task. 

The probe kinetic methodology developed by Scaiano [23] to study radicals and biradicals by laser flash photolysis (LFP) methodology is readily extended to carbenes. LFP (308, 337, 351, or 355 nm) of diazirine or diazo compounds in the presence of pyridine produces carbenes, which generally react rapidly lO M sec" ) to form ylides. [28,29] Ylides are much easier to monitor than the carbenes because they have intense UV-Vis absorption and microsecond lifetimes. Pyridine ylide methodology has enabled LFP studies of alkyl, dialkyl, alkylhalo, dihalo and carbonylcarbenes. It is now a standard tool and will be used as long as LFP studies of simple carbenes are performed. 

Thermolysis or photolysis of diazoalkanes (equation 3.6) and dialkyl-diazirines (equation 3.7)... 

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