A cascade [3+2] annulation, involving a γ-selective vinylogous Michael addition of nitroalkylideneoxindoles to various electron deficient alkenes followed by an intramolecular Michael addition, provides access to dispiro-bis-oxindoles and spirooxindoles. Up to four contiguous chiral centers, including two quaternary spirocenters, are generated in this high-yield regio-and diastereoselective transformation that also provides a convenient entry into conformationally constrained γ-amino acid derivatives.S pirocyclic oxindole belongs to one of the leading and most diverse classes of frameworks present in numerous natural products, 1 for instance, prosurugatoxin I, 2 neosurugatoxin II, 3 surugatoxin aglycone III, 4 citrinalin A and B IV, 5 and cyclopiamine A and B V (Figure 1). 6,7 These spiro compounds
An enantioselective desymmetrization of curcumins with 3‐olefinic oxindoles involving a cascade double‐Michael addition strategy provides direct access to spirocyclohexanone‐oxindoles with complete regio‐ and diastereoselectivities and excellent enantioselectivities, besides good to excellent yields. The products possess three contiguous chiral centers and multiple reactive functionalities. The observed selectivities were rationalized by transitions state energy calculations at B3LYP//6‐31g(d) level of DFT.
A convenient protocol for the synthesis of spirobenzofuran-isobenzofurans
and substituted benzofurans via a modified Hauser–Kraus reaction
of 3-sulfonylphthalide with 2-formylaryl triflates is reported here.
The initial reaction involved 1,2-addition of phthalide to the formyl
group and intramolecular cyclization via substitution of triflate
followed by a cascade of rearrangements leading to spirolactone or
benzofuran derivatives. The electronic nature of substituents on aryl
triflates affected the course and outcome of the reaction. The mechanism
was supported by successful characterization of one of the intermediates
by mass spectrometry. A medicinally relevant influenza virus type
B inhibitor, benzofuroisocoumarin, was synthesized in a single step
from the spiro compound, thus demonstrating the synthetic utility
of our methodology.
An unusual Morita–Baylis–Hillman (MBH) type reactivity of isatin‐derived nitroalkenes with activated carbonyl compounds has been demonstrated for the first time. The unexpected 3‐alkylideneoxindole esters were formed in moderate to excellent yields with complete stereoselectivity (only E‐isomer). The proposed mechanism based on control experiments involves a hybrid MBH–Wittig pathway.
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