Dieckmann cyclizations of unsymmetrical diesters in polymer supports and in solution

Abstract

Polystyrylmethyl triethylcarbinyl adipate ( 1f) was prepared from crosslinked polystyrenes containing 10% divinylbenzene (DVB) and 25% chloromethylstyrene (VBC), 10% DVB and 10% VBC and 6% DVB and 10% VBC. Treatment of the polymeric mixed diesters with potassium t-butoxide in dimethylformamide (DMF) and with potassium triethylcarbinolate in DMF gave about 75% yields of triethylcarbinyl 2-cyclopentanonecarboxylate ( 7f) from Dieckmann cyclization. The analogous benzyl triethylcarbinyl adipate ( 1e) cyclized in good yield using a variety of solvent-base conditions. Treatment of 1f with lithium bis(trimethylsilyl)amide in tetrahydrofuran gave 81% of benzyl 2-cyclopentanonecarboxylate ( 6f) and 6% of 7f, indicating product control during irreversible formation of the less hindered lithium enolate. Of the many successful solvent-base combinations for cyclization of the soluble diester 1e, only the potassium alkoxides were satisfactory for cyclization of the polymeric diester 1f. Treatment of diethyl hexadecanedioate with potassium t-butoxide in boiling xylene followed by hydrolysis and decarboxylation gave 39% of cyclopentadecanone, but attempted Dieckmann cyclizations of the dimethyl, benzyl triethylcarbinyl and polystyrylmethyl triethylcarbinyl esters of hexadecanedioic acid gave predominantly products of transesterification.