Enolic Ortho Esters. II. Tandem Nucleophilic Electrophilic Dimethylation of 4',4'-Dimethyl-3,4,5,8-tetrahydrospiro[2H-1-Benzopyran-2,2'-[1,3]dioxolan]

Abstract

Reaction of 4′,4′-dimethyl-3,4,5,8-tetrahydrospiro[2H-1-benzopyran-2,2′-[l,3]dioxolan](9) with methylmagnesium iodide in benzene or toluene at 40º gave the iodomagnesium enolate acetal (10) which upon in situ reaction with methyl iodide afforded 56% of pure 6 ξ-methyl- 6-[2′-(2″,4″,4″-trimethyl-1″,3″-dioxolan 2″yl)ethyl]cyclohex-3-en-one (11), the product of tandem nucleophilic/electrophilic dimethylation . Aqueous ammonium chloride workup of the iodomagnesium enolate (10) gave 6-[2′-(2″,4″,4″-trimethyl-1″,3″-dioxolan 2″yl)ethyl] cyclohex-3-en-1-one (7).

Some further transformations of the methylated keto acetal (11) are described.