Abstract 4‐Methyl‐4‐penten‐2‐ol reacts in acidic medium with acetaldehyde to give a mixture of r ‐2, cis ‐4‐, cis ‐6‐, & r ‐2, trans ‐4, cis ‐6‐trimethyl‐4‐tetrahydropyranol (2) and r ‐2, cis ‐4‐, cis ‐6‐, & r ‐2, trans ‐4, cis ‐6‐trimethyl‐4‐(4′‐methylidene‐2′‐pentoxy)‐tetrahydropyrane (3). The third possible isomer, the trans ‐2, 6‐dimethyl derivative, could not be detected. This stereochemical outcome strongly suggests a hemiacetal intermediate. The dehydration products of 2, cis ‐2,6‐dimethyl‐4‐methylidene‐tetrahydropyrane (5) trans ‐and cis ‐2, 4, 6‐trimethyl‐5, 6‐dihydro‐2, pyrane (6 and 7) are reported. A half‐chair form for 6 follows from its 1 H‐nmr spectrum.
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Tavernier et al. (1976) studied this question.
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