Attempts to prepare an all-carbon indigoid system

Abstract

SummaryFirst attempts are described to prepare a precursor for an all-carbon analog of indigo, the tetracyclic triene 4. Starting from indan-2-one (9) the α-methylene ketone 13 was prepared. Upon subjecting this compound to a McMurry coupling reaction, it dimerized to the bis-indene derivative 17, rather than providing the tetramethyl derivative of 4, the hydrocarbon 14. In a second approach, indan-1-one (18) was dimerized to the conjugated enedione 21 through the bis-1-indene dimer 19. All attempts to methylenate 21 failed, however. When 19 was treated with the Tebbe reagent, the dimer 23 was produced, presumably through a Cope reaction of the intermediately generated isomer 22. The bis-indene derivative 23 can be alkylated with 1,2-dibromoethane to produce a 1:1 mixture of the spiro compounds 24 and 25. Although 9 could be reductively dimerized to 30, the conversion of this olefin to 14 failed.

Strategies for the Synthesis of Chiral Carbon‐Bridged Group IV ansa‐Metallocenes

“…Substituted ebi ligands were prepared through alternative synthetic routes such as a reductive homocoupling of benzofulvene, or a Pauson–Khand approach (see below) . In addition, the formation of unsubstituted ethylenebis‐indene by a Cope rearrangement of a dimethylene biindene was observed . However, the main route to substituted derivatives remained the double nucleophilic substitution at the termini of a bridge building block by a deprotonated indene derivative.…”

“…[50] In addition, the formation of unsubstitutede thylenebis-indene by a Cope rearrangemento fadimethylene biindene was observed. [51] However,t he main route to substituted derivatives remainedt he doublen ucleophilics ubstitution att he termini of ab ridge building block by ad eprotonated indened erivative. For example, ap ropylene-bridged titanocene-analogue and an ortho-xylylene-bridged Zr-analoguew ere prepared.…”