Transient hydroboration and hydroalumination of activated azo-species: avenues to NBO and NAlO-heterobicycles

Abstract

Reactions of the boranes, BH(C6F5)2 or 9-BBN, with azodicarboxylates or an azodicarbonylamide provide facile access to NBO heterocyclic compounds. The products [C6F5)2BOC(X)N]2 X = OEt, 1, OiPr 2, OCH2Cl3C 3,...

The impact of Lewis acid variation on reactions with di-tert-butyl diazo diesters

“…This structure is directly analogous to those previously reported for reactions of other diazo esters with secondary boranes. 21 In addition it is analogous to the product reported for the thermal reactions of BPh 3 and ( t BuO 2 CN) 2 . 21 In this case, it is interesting to note that the steric demands of the t Bu-diazo ester do impact on the course of the hydroboration which affords 1 .…”

“…This structure is directly analogous to those previously reported for reactions of other diazo esters with secondary boranes. 21 In addition it is analogous to the product reported for the thermal reactions of BPh 3 and (tBuO 2 CN) 2 . 21 In this case, it is interesting to note that the steric demands of the tBu-diazo ester do impact on the course of the hydroboration which affords 1.…”

“…Initial reactions of diazo diesters of the form (RO 2 CN) 2 (R = Et, iPr, CH 2 CCl 3 , and CH 2 Ph) with secondary boranes afforded heterobicyclic products via hydroborations (a, Scheme 2(a)). 21 In contrast, we showed that reactions of (EtO 2 CN) 2 with phosphine/borane FLPs afforded either 1,2 or 1,4 additions of FLPs across the NN or OCNN fragments (b, Scheme 2(b)). 22 The use of the sterically encumbered diazo diester ( t BuO 2 CN) 2 with B(C 6 F 5 ) 3 liberated methylpropene and CO 2 giving the diazeneborane adduct (N 2 H 2 )(B(C 6 F 5 ) 3 ) 2 which is transformed into the hydrazine adduct (N 2 H 4 )(B(C 6 F 5 ) 3 ) 2 on standing (Scheme 2(c)).…”

Addition and NN bond cleavage of diazo-compounds by phosphino-phosphenium cations

“…In our own efforts, we showed that while species of the form (RO 2 CN) 2 (R = Et, iPr, CH 2 CCl 3 , CH 2 Ph) undergo hydroboration affording heterobicyclic products, 9 they also react with FLPs to give either 1,2 or 1,4 additions of FLP across the NN, or OCNN fragments depending on the nature of the FLP (Scheme 1). 10 Interestingly, the corresponding reaction of the more sterically encumbered diazo diester ( t BuO 2 CN) 2 with B(C 6 F 5 ) 3 liberates isobutylene and CO 2 affording the diazene-borane adduct (N 2 H 2 )(B(C 6 F 5 ) 3 ) 2 which transforms to the hydrazine adduct, (N 2 H 4 )(B(C 6 F 5 ) 3 ) 2 (Scheme 1).…”

Reactivity of frustrated Lewis pairs with BOC protected diazocarboxylates: FLP capture of diazene

“…Most recently, we have described the reactions of boranes with diazodiesters. While reactions of sterically unencumbered diazo-diesters afford heterocyclic products, 21 the reaction of the sterically encumbered diazo-diester ( t BuO 2 CN) 2 with B(C 6 F 5 ) 3 results in the liberation of methyl-propene and CO 2 affording the diazene-borane adduct (N 2 H 2 )(B(C 6 F 5 ) 3 ) 2 which is slowly converted to the analogous hydrazine adduct. 22 Further, these species react with basic phosphines to give the corresponding anions [(N 2 H)(B(C 6 F 5 ) 3 ) 2 ] − and [(N 2 H 3 )(B(C 6 F 5 ) 3 ) 2 ] − , respectively (Fig.…”