The blueprint for this AHOM idea is shown in Figure . An appropriately substituted diazene catalyst 3 can undergo alkylation by an alkyl halide 1 to form diazenium 6. N-Alkyldiazeniums can tautomerize to form the corresponding hydrazoniums 7, thus intersecting with our carbonyl-olefin metathesis strategy. [3+2]-cycloaddition of hydrazonium 7 with the olefin substrate 2 produces an intermediate pyrazolidine cycloadduct 8. Due to the symmetry of this intermediate, cycloreversion to alternative, metathesized fragments in the form of olefin 4 and hydrazonium 9 can occur. In theory, tautomerization of 9 to diazenium 10 followed by dealkylation by the halide counteranion would lead to the new alkyl halide product 11 and regenerate the diazene 3. In practice, however, we have found that hydrolysis of 9 outcompetes this pathway, which leads instead to the formation of a carbonyl product 5. Although this hydrolysis necessarily returns the catalyst in its reduced form as hydrazine 12, the autoxidation of hydrazines is usually quite facile. Thus, adventitious oxygen can lead to oxidation to reform the diazene 3. Given this behavior, we have termed this reaction oxidative alkyl halide-olefin metathesis. We began our investigation of this concept by examining the ring-closing metathesis of alkenyl bromide 13c (Figure ). For reference, 13c spontaneously undergoes a Prins-type cyclization under thermal conditions, leading to the formation of 9-isopropylphenanthrene (14). However, in the presence of 2,3-diazabicyclo[2.2.2]oct-2-ene (17) or benzo [c]cinnoline (18) under various conditions described below, 13c converted instead to phenanthrene (15) and acetone (16c), the products of the oxidative ring-closing alkyl halide-olefin metathesis. In the development of this AHOM reaction, we first examined the effect of the alkene substituents by screening several different olefins, 13a-c (Table ). Using 1 equiv diazene 17 and a reaction temperature of 65 °C in MeCN, all three substrates converted to phenanthrene in nearly quantitative yield (entries 1-3), with the isopropylidene substrate 13c requiring the shortest reaction time (entry 3). Unfortunately, we were unable to achieve catalyst turnover with 17, which we believe was due to the difficulty of reoxidizing the protonated hydrazinium intermediate (cf. 12, Figure ). To remedy this situation, and to identify a catalyst with greater potential for electronic tuning, we examined benzo [c]cinnoline 18 (BCC) as an alternative diazene. We had previously demonstrated the utility of BCC as a catalyst for the oxidation of alkyl halides to aldehydes, 17 in which turnover was readily achieved by autoxidation with adventitious O2, and we reasoned that the spontaneous oxidation of BCC should enable a catalytic reaction. Olefins 13a-c were again screened with stoichiometric 18 to determine the most reactive olefin (entries 4-6). In this case, olefin 13b was found to be optimal, leading to phenanthrene (15) in 85% yield. Interestingly, the cis-isomer was more reactive than the trans, which we suspect may be due to steric strain between the benzocinnoline framework and the trans olefin substituent inhibiting the cycloaddition step. While olefin 13c was determined to be the most reactive substrate with diazene 17, the use of 18 led primarily to 9isopropylphenanthrene ( ) as the major product instead of the metathesis adduct 15. We speculate that 18, being less electron-rich, has a slower rate of alkylation, which thus leads to the competitive formation of the undesired side-product. After identifying the most productive olefin substrate, we examined the possibility of catalysis with 18 (Table ). Treatment of 13b with 20 mol% 18 at 100-120 °C for 48 h led to the formation of phenanthrene (15) in varying yields (entries 1-5), with MeCN being optimal (entry 6). In all cases, adventitious water and O2 were sufficient to induce catalyst turnover. Reducing catalyst loading (entries 7 and 8) was detrimental to yield.