Ninhydrin as a Source of Naphthoquinone Acetals and Benzocycloheptenetrione Derivatives, and the Trapping of an Oxacarbene Derived from a Cyclopentanone

Abstract

1,3‐Bis(ethylenedioxy)‐2‐indanone (2) was shown to react with some dienophiles to give naphthoquinone acetals under photochemical reaction conditions, presumably by photodecarbonylation via the corresponding ortho‐quinodimethane. With maleic anhydride the highly oxygenated benzocycloheptane derivative rac‐12 was obtained in good yield. In a similar manner, upon irradiation in the presence of acrylonitrile a 2:1 mixture of ring‐expanded regioisomers rac‐13 and rac‐14 was obtained. Irradiation in the presence of fumarodinitrile unexpectedly gave the spirocyclic compound rac‐15, which was characterized by X‐ray crystallography. rac‐15 is the trapping product of oxacarbene 16, thus demonstrating a rare case of a ring expansion of a cyclopentanone to give a six‐membered ring oxacarbene, here leading to an orthoester. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Total synthesis of the aglycone of IB-00208

“…Toward this end, the known benzocyclobutenedione 22 was selected as a substrate because it possessed an aryl group fused to a cyclobutenone, was symmetrical, and was readily accessible (Scheme 5). 22 Deprotonation of alkyne 17 using n -BuLi followed by addition of the resultant anion to 22 provided the 1,2-addition product, which was treated with HF·pyridine to remove the cyclic silyl group to furnish 23 in 48% yield over two steps. Unfortunately, attempts to oxidize the secondary alcohol in 23 were unsuccessful, perhaps owing to the instability of the ynone product.…”

Wavelength dependent photoextrusion and tandem photo-extrusion reactions of ninhydrin bis-acetals for the synthesis of 8-ring lactones, benzocyclobutenes and orthoanhydrides

“…Wavelength dependent photoextrusion and tandem photo-extrusion reactions of ninhydrin bis-acetals for the synthesis of 8-ring lactones, benzocyclobutenes and orthoanhydrides † The photodecarbonylation of ninhydrin bis-acetal 2 to benzocyclobutene 3 was developed by Butenscho ¨n et al to provide low cost access to benzocyclobutenedione (Scheme 1). 1 Indeed, it remains the most convenient method for its synthesis in spite of the modest yield attained for the photoextrusion of carbon monoxide from 2. Consequently, when a need for benzocyclobutenedione arose, we decided to develop the reaction as a flow photochemical process in order to facilitate its optimisation with respect to wavelength, residence time, solvent and acetal protecting group.…”

“…S1b and c, ESI †). The observed transient spectrum at 1 ps time delay showed an absorption band at 585 nm which was assigned to the np* (S 1 ) excited state 1 [4a] following comparison of the extracted spectrum with that computed for the S 1 state (Fig. S7, ESI †).…”

“…19 Thus, the wavelength dependence of the reaction centres on the fate of longlived intermediate 26 (Scheme 4). Irradiation of 26 with UVA leads to a singlet excited state 1 [26] that can relax to benzocyclobutene 24. By contrast, its irradiation with UVB or UVC light gives rise to higher singlet excited states of 26 from which ISC to 3 [23] is allowed.…”

“…Applying this mechanistic understanding to ninhydrin bisacetal 2 (Scheme 5) led us to conclude that the course of that reaction was also dictated by the nature of the excitation of quinodimethane intermediate 28. As before, its irradiation with UVA gives a singlet excited state 1 [28] from which benzocyclobutene 3 is derived. Similarly, irradiation with UVB or UVC light leads to biradical 3 [29], which in turn collapses to biradical 30.…”