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2 Wełniak M.

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Novel Rearrangement of Tertiary Fenchyl Alcohols with Sulfuric Acid in Acetonitrile

Wełniak M.

Polish Journal of Chemistry

2002

Vol. 76 / nr 1

37-44

The influence of steric hindrance on rearrangements of tertiary 2-fenchyl cations under the Ritter reaction conditions (CH3CN/H2SO4) has been described. Depending on the branching of alkyl substituents at the C-2 position, the reaction time and temperature, different reaction courses have been observed. After 10 minutes at -20 to -15°C alcohol 2 (R = iso-Am) gave alkenes 7, whereas a pair of amides 8 and 9 for 24 hours at ambient temperature as a result of successive exo-3,2-methyl shift,Wagner-Meerwein rearrangement and endo-6,2-hydride shift. Alkene 10 was obtained as a primary product from alcohol 3 (R = iso-Bu) after 10 minutes at -20 to -15°C. When the same reaction was continued for 24 hours at room temperature, amide 12 has been obtained as the only product. It was explained by the operation of endo-6,2-hydride shift after protonation of alkene 10 and further reaction with acetonitrile. In the case of alcohols 4-6 with bulky isopropyl, sec-butyl and 2-sec-amyl substituents, a novel rearrangement to tetrasubstituted alkenes containing the bicyclo[3.1.1]heptane skeleton have been notified. The mechanistic proposals for the investigated reaction are presented.

The Ritter reaction of terpenes. Part 2. The fenchyl system

Wełniak M.

Polish Journal of Chemistry

1998

Vol. 72, nr 6

1021-1027

The Ritter reaction of fenchyl alcohols 2a-f was examined. Surprisingly, in the case of alcohols 2a-d, formation of the corresponding alkenes 3 was observed. These compounds underwent, in turn, Namietkin and Wagner-Meerwein rearrangements, followed by endo-6,2-hydrogen shift to give acetamides 8 and 9, The alcohol 2e gave a mixture of hydrocarbons 11 and 12 as well as an anti acetamide 9e. For secondary ando-2-fenchol (2f) exo-isofenchyl acetamide (15) was the only product as a result of endo-6,2-hydrogen shift and subsequent reaction with acetonitrile.