The cycloaddition of dichloroketen with indene: a new synthesis of 4,5-benzotropolone

One hundred years of benzotropone chemistry

“…Condensation of 27 with methoxyacetone in the presence of NaOH and then cleavage of the methyl ether 243 by strong acid afforded 2-hydroxy-4,5-benzotropone ( 238 ). Turner’s group reported a new method for the synthesis of 4,5-benzotropolone ( 238 ) via the cycloaddition of dichloroketene (generated in situ from trichloroacetyl chloride) with indene followed by hydrolysis of the adduct 244 with sodium acetate in aqueous acetic acid ( Scheme 38 ) [ 158 ]. In addition, Stevens’ group reported a method for the synthesis of 238 using a strategy similar to that of Turner’s group ( Scheme 38 ) [ 159 ].…”

Rearrangement of the hindered cyclobutadiene from dimerization of 3,3,6,6-tetramethylcyclohexyne

“…The reaction solution, maintained at a temperature of 15-20°, was then irradiated with a Sylvania sunlamp until no further color change was noted (ca. 3 hr). The resulting light yellow solution was shaken with a dilute sodium bisulfite solution, twice with a saturated sodium chloride solution, and dried over magnesium sulfate.…”

Preparation of Conformationally Constrained α2‐Antagonists: The Bicyclo[3.2.0]heptane Approach

“…The bicyclo[3.2.0]heptane system is commonly derived from an intermolecular [2+2] cycloaddition between an indene‐type substrate and a dichloroketene,2 or another ketene equivalent 3. Herein, we report a novel approach to the key benzo‐fused bicyclo[3.2.0]heptane intermediates 2 (Scheme ), and disclose our full synthetic studies towards the prototypic molecules 1 , in which R = H and R = CH 3 (Figure 1).…”