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45.7.2.1.1.1.1 Variation 1: Reduction of (Dihalomethyl)cyclohexadienones with Polymer-Bound Dibutyltin Hydride

DOI: 10.1055/sos-SD-045-00240

Abou-Hadeed, K.; Hansen, H.-J.Science of Synthesis, (201045339.

Tributyltin hydride is an excellent and broadly applicable radical-reducing agent for CX bonds; however, it is not always easy to remove tin-containing material from the mixture of products. One solution to this dilemma is the development of a polystyrene-based polymer-bound tin hydride of the general formula [resinC6H4(CH2)2SnHBu2]. This polymer is insoluble in common organic solvents, and can be filtered off easily after each reaction and regenerated with dibutylaluminum hydride in tetrahydrofuran.[‌53‌,‌54‌] Indeed, tropones 32, 33, and 34 can be prepared from 2- and 4-(dichloromethyl)-substituted dienones with the polymer-supported tin hydride without loss in yield, but with prolonged reaction times. Some examples are listed in Scheme 11.[‌55‌] Are there other reducing agents for tropone formation? There are at least two reports in the literature that 2-methyltropone (32, R1=R2=R3=H) can also be formed from 6-(dibromomethyl)-6-methylcyclohexa-2,4-dien-1-one with tetrakis(triphenylphosphine)nickel(0)zinc in benzene (74% yield),[‌56‌] or with zinc in dimethylformamide (60% yield).[‌57‌]

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