Synthesis of Annulated Anthracenes, Carb­azoles, and Thiophenes Involving Bradsher‐Type Cyclodehydration or Cycli­zation–Reductive‐Dehydration Reactions

Abstract

A conventional BF 3 ·OEt 2 -mediated Bradsher-type cyclodehydration of 2-arylmethyl benzaldehydes in CH 2 Cl 2 at room temperature gave polycyclic aromatic and heteroaromatic compounds. Alternatively, these compounds could be syn-

Reductive Aromatization/Dearomatization and Elimination Reactions to Access Conjugated Polycyclic Hydrocarbons, Heteroacenes, and Cumulenes

“…A straightforward example of acene synthesis with this two‐step protocol uses acenones synthesized by cyclization of 2‐benzylbenzoic acids, such as functionalized 2,5‐dibenzyl terephthalic acids (Scheme ). Once again, the aromatization was performed using NaBH 4 followed by treatment with HCl, or using Al(O‐ i Pr) 3 (generated in situ) as the reducing agent (Section 6.1).…”

“…[198] Compounds obtained via this two-stepp rocedure include anthracene 134 [199] and 135 a,b, [200] tetracene, [201] and pentaphene 136 (Scheme55), [200b] as well as others. [199,200,202] As traightforward example of acene synthesis with this twostep protocol uses acenones synthesized by cyclization of 2benzylbenzoic acids, [203] such as functionalized2 ,5-dibenzyl terephthalic acids (Scheme 56). Once again,t he aromatization was performed using NaBH 4 followed by treatmentw ith HCl, [204] or using Al(O-iPr) 3 (generated in situ) as the reducing agent (Section6.1).…”

Recent advances in the syntheses of anthracene derivatives

“…By using both methodologies, the authors obtained substituted benzo[ a ]anthracenes from compounds 83 . In 2015, Mohanakrishnan’s group also disclosed a Bradsher-type cyclodehydration of substituted 2-arylmethylbenzaldehyde 85a mediated by BF 3 ·OEt 2 ( Scheme 21 ) [ 55 ]. By using this methodology, they prepared substituted anthracene derivatives 86 in excellent yields (75–93%).…”

Semicarbazide: A Transient Directing Group for C(sp3)−H Arylation of 2‐Methylbenzaldehydes

“…Benzylbenzaldehydes are critical building blocks in the construction of a variety of fused rings, [11] natural products, [12] and biologically active compounds. [13] Numerous synthetic protocols have been successfully demonstrated for 2-benzylbenzaldehydes, including the traditional oxidation of 2-benzylbenzyl alcohols, [14] the reduction of N,N-dimethylcarboxamides, [15] and the rearrangement of aromatic alcohols.…”

“…The addition of 50 μL of water slightly improved the yield (entries 8, 9), attributing to that water probably could promote the hydrolysis of the possibly formed semicarbazone and regeneration of semicarbazide under acidic conditions. Compared with Pd(OAc) 2 , Pd (PPh 3 ) 2 Cl 2 as a catalyst could increase the yield of 3 a to 61% while PdCl 2 , Pd(TFA) 2 , and Pd(dppf)Cl 2 achieved inferior performance (entries [10][11][12][13]. The other transition metal catalysts, such as Cu(OAc) 2 , FeCl 2 and Ni(OAc) 2 , were also checked but no catalytic effect on the reaction (entries [14][15][16].…”