Page 51 - Read Online
P. 51
Yang et al. Chem Synth 2023;3:7 https://dx.doi.org/10.20517/cs.2022.38 Page 15 of 54
Scheme 17. Benzolactones 36 as 1C synthons for construction of chiral spirolactones.
Scheme 18. Aminocatalytic cascade reaction of enals 37 with benzofuranones 36. This figure is used with permission from Wiley-VCH
Verlag [51] .
The plausible mechanism for organocascade was proposed. It is initiated with an iminium-catalysed
Michael addition of 36 to 37 in the presence of C8 to give intermediate I. A second iminium-mediated
Michael addition of the chiral nucleophilic intermediate I to another molecule of enal 37 is expected to give
intermediate II. Lastly, an enamine-driven intramolecular aldol reaction of II followed by dehydration led
to the formation of spirocyclic benzolactone 38 with excellent stereoselectivities [Scheme 18].
[60]
In addition, in 2010, Companyó et al. developed an aminocatalytic Michael-Michael-aldol reaction,
affording spirocyclic derivatives in good yields and in almost diastereo- and enantiopure form. However,
only one example was reported that utilized benzolactone as a 1C synthon to afford the chiral spiro
benzolactone compound in 93% ee and > 25:1 dr.
