%0 Generic
%9 Master's Thesis
%A Berne, Alexander M
%D 2015
%F pittir:25965
%K Nazarov, cyclization, dienyl sulfone, vinyl sulfone, allyl sulfone, tetrahydrofluorene, cyclobutene, electrocyclic ring opening, electrocyclization 
%T A Formal Vinyl Sulfonyl Nazarov Cyclization Accesses 9-(tosylmethyl)-2,3,4,4a-tetrahydro-1H-fluorenes
%U http://d-scholarship-dev.library.pitt.edu/25965/
%X During the course of a proposed route to synthesize ladderane lipids, a novel one-pot 4π electrocyclic ring opening followed by a Nazarov-type 4π electrocyclization reaction was discovered. The reaction was studied further due to its potential as a method for accessing the privileged tetrahydrofluorene scaffold and the opportunities for further functionalization provided by the allyl sulfone moiety. Optimized conditions for the transformation involved refluxing model substrate 7-phenyl-8-tosylbicyclo[4.2.0]oct-6-ene in 1,2-dichloroethane for 3 h to generate intermediate (E)-1-((2-(cyclohex-1-en-1-yl)-2-phenylvinyl)sulfonyl)-4-methylbenzene. Upon cooling to room temperature, addition of 1.2 equiv iron(III) chloride promotes cyclization to furnish 9-(tosylmethyl)-2,3,4,4a-tetrahydro-1H-fluorene after 10 h in 78% yield. In order to determine the effect electronics may have on the transformation, functionality was introduced onto the phenyl ring. While no noticeable effect was observed on the electrocyclic ring opening step, the nature of the substituents significantly affected the quantity of promoter required for the cyclization step. Although a superstoichiometric amount of iron(III) chloride and heat was required with an electron withdrawing substituent on the aryl ring, electron donating substituents lowered the activation barrier to cyclization – necessitating only catalytic amounts of iron(III) chloride at room temperature. This transformation represents the first report of a Nazarov cyclization with a vinyl sulfone on the central carbon.