Adduct of NacNacAl with Benzophenone and Its Coupling Chemistry

Abstract

Reaction of NacNacAl (NacNac=[DippNC(Me)CHC(Me)NDipp]−) with one equivalent of benzophenone affords a ketylate species NacNacAl(η2(C,O)‐OCPh2) that undergoes easy cyclization reactions with unsaturated substrates. The scope of substrates included benzophenone, aldimine (PhNC(Ph)H), quinoline, phenyl nitrile, trimethylsilyl azide, and a saturated cyclic thiourea. The latter substrate reacted by an unusual C−N cleavage that left the C=S functionality intact. The new products were characterized by NMR spectroscopy and X‐ray diffraction analysis.

Selective Cross‐Coupling of Unsaturated Substrates on AlI

“…In previous work, we reported that the benzophenone complex 3 reacts with quinoline to give the C−C coupling product 4 (Scheme 1). [14] We have now established that reaction of the Al I compound 1 with a mixture of benzophenone and pyridine gives chemoselectively the analogous coupling product 5 (Scheme 2). This result is significant because 1 instantaneously reacts with both of these substrates independently: in the case of benzophenone it affords the adduct 3 or pinacolate NacNacAl(OCPh 2 ) 2 (if two equivalents of benzophenone are used), and with pyridine it gives a red gel of unknown composition [8b] .…”

“…[20] Furthermore, with oxidizing bases,s uch as quinoline, reaction with 1 resultsi nt he CÀCc oupling of heterocycles. [14] But al ess oxidizing andm ore basic heterocycle such as DMAP, leads to backboned eprotonation. [8b] It becomes,c lear that for fenchone, which can be regarded as aw eak but oxidizing base, the main mode of reactivity with Al I is charget ransfer to the carbonyl moiety,l ikely creatingabiradicaloid.…”

“…[12] Our interesti nt his area was mo-tivated by two separate observations:W eo bservedc oupling of isocyanates and diimides on the Ga I compound NacNac-Ga, [13] and secondly, we discovered sequential coupling of the isolable benzophenone adduct NacNacAl(h 2 (O,C)-OCPh 2 )( 3) with unsaturated substrates that include carbonyls, imines,n itriles, and even heterocycles, (Scheme 1d). [14] These findings posed the questionast owhether the chemoselectivec oupling of two different unsaturated molecules on am ain-group center could be possible. Herein we providea na nswer to this question and report the first examples of such acoupling.…”

Shedding Light on the Diverse Reactivity of NacNacAl with N‐Heterocycles

“…However, there has been no prior example of such a coupling on a single carbenoid center. Nevertheless, the chemistry outlined in Scheme is somewhat reminiscent of the coupling of quinoline with the benzophenone adduct NacNacAl(η 2 (C,O)‐O=CPh 2 ), which results in C−C bond formation at the 2‐position of the quinoline . It further suggests that a charge transfer from the electron‐rich Al I species 1 to an N‐heterocycle and/or formation of a singlet biradical species may be responsible for the chemistry illustrated in Scheme and Scheme .…”

The Aluminyl Anion: A New Generation of Aluminium Nucleophile

“…The chemistry of 2 , in particular, is undergoing a recent renaissance, being a key reagent in a number of recent publications [12] . These recent reports include the activation of small molecules (CO, C 2 H 4 ), [12c,j] reduction chemistry (including that of benzene), [12b,e,i,k,m] cycloadditions [12a,d,g] and various bond activations including C−H and C−F [12c,f,h,l,n] . The vast majority of the reactions of 1 and 2 are best described as oxidative additions, although some evidence of nucleophilic behaviour has been reported (especially with electropositive metals/Lewis acids) and this has been exploited in the formation of Al‐metal donor/acceptor bonds [11] .…”