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29.9.1.1.1.7.2 Variation 2: Aromatic Anion Addition

DOI: 10.1055/sos-SD-029-00536

Ley, S. V.; Milroy, L.-G.; Myers, R. M.Science of Synthesis, (200729644.

Efficient entry to a range of aryl spiroketals can be obtained using benzamides as precursors. As shown in the examples in Scheme 33, diethylbenzamides 109 undergo selective ortho-lithiation when treated with tert-butyllithium containing N,N,N,N-tetramethylethylenediamine and on addition to lactones 110 afford the intermediate oxo alcohol 111.[‌138‌] Cyclization to the aryl spiroketals 112 is achieved using catalytic 4-toluenesulfonic acid, since trifluoroacetic acid, perchloric acid, and hydrochloric acid in this instance all fail to provide the acidic conditions required to initiate spirocyclization.

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