A Convenient Synthesis of 2,3-Benzotropone from α-Tetralone by Ring-expansion

Abstract

2,3-Benzotropone (1) has conveniently been prepared from easily available α-tetralone (2) in good overall yield by the following successive reactions: dihalocarbene addition to enol-ether (3) derived from 2, ring-expansion of the adduct (4) to halobenzocycloheptadienone (5), and dehydrohalogenation of 5 giving 1.

One hundred years of benzotropone chemistry

“…3.1.2. Other synthetic approaches: A convenient synthesis of 2,3-benzotropone ( 12 ) from α-tetralone ( 171 ) by ring expansion was performed by Sato’s group ( Scheme 31 ) [ 140 ]. First, 1-ethoxy-3,4-dihydronaphthalene ( 172 ) was prepared by reacting α-tetralone ( 171 ) with ethyl orthoformate in the presence of an acid catalyst.…”

First Total Synthesis of the Benzotropolone/Bis(pulvinone) Natural Product Aurantricholone Exploiting New Strategies for Establishing Benzotropolones andZ‐Configured Pulvinones

“…This idea emerged from reading a review entitled “One hundred years of benzo tropone chemistry” [24] . Its Scheme 31 showed how unsubstituted tetralone ( 27 ) had led to unsubstituted benzo tropone ( 40 ) in four operations and five steps (Scheme 4, column 2) [25] . The intermediates of this transformation had been an enol ether (not depicted), the dibromocyclopropane 30 , the ring‐expanded 2‐bromo‐2‐en‐1‐one 34 , and an equilibrium portion of its C=C‐shifted isomer 38 [25] …”

“…2) The arylbutyric acid 25 also is a 4‐substituted veratrole, and compounds of that kind are readily brominated at C‐5. Having recognized this, we turned to the question of how to divert the benzotropone‐forming tetralone‐expansion 27 →→→→ 40 [25] (Scheme 4, column 2) to the benzotropolone‐forming tetralone‐expansion 24 →→→→ 23 (Scheme 4, line 1) which we needed en route to aurantricholone ( 3 ). It turned out helpful to complement the findings of column 2 with more reactions from the literature.…”

“…By consequence, they should be susceptible, for instance, to Kornblum oxidations, [28] which were developed, inter alia, as a “Convenient Synthesis of Glyoxals, Glyoxalate Esters, and α‐Diketones” [28c] . The bromide 38 , which hitherto 1,4‐eliminated giving benzotropone ( 40 ) [25] (Scheme 4), might be scavenged by a Kornblum oxidant (even) faster. Thereupon, the α‐diketone 37 should form – and tautomerize giving benzotropolone ( 1 ) as we desired.…”

Origin of the preference for the chair conformation in the Cope rearrangement. Effect of phenyl substituents on the chair and boat transition states

“…treatment of 1-tetralone (1) with triethyl orthoformate and a catalytic amount of concentrated HC1 gave the ethyl vinyl ether 4 in 78% yield. 20 Conversion of 1 to the trisylhydrazone 2 followed by a Shapiro reaction21 using DMF as the electrophile afforded the ,/3-unsaturated aldehyde 3 (65%). DIBALH reduction of aldehyde 3 gave the allylic alcohol 5.22…”