Synlett 2010(15): 2319-2321  
DOI: 10.1055/s-0030-1258025
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Improved Synthesis of the Pheromone of the Longtailed Mealybug

Yunfan Zou*, Jocelyn G. Millar
Department of Entomology, University of California, Riverside, CA 92521, USA
Fax: +1(951)8273086; e-Mail: yunfanz@ucr.edu;
Further Information

Publication History

Received 14 May 2010
Publication Date:
30 August 2010 (online)

Abstract

A short and efficient synthesis of the longtailed mealybug pheromone featuring an Ireland-Claisen rearrangement as the key step is described.

    References and Notes

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9

In ref. 8c and 8d, the α,β-unsaturated ester was reacted with hot polyphosphoric acid for 10 min and 3 min, respectively, before the reaction was stopped. However, in our hands, only starting material was recovered with such short reaction times. We found the reaction to be complete after ca. 5 h, which is more consistent with ref. 8a and 8b.

10

When AcCl was used instead of Ac2O, the yield was lower (65%).

11

Data for Acetic Acid 3,4,4-Trimethyl-cyclopent-2-enyl Ester (6) ¹H NMR (400 MHz, CDCl3): δ = 5.50 (m, 1 H), 5.33 (m, 1 H), 2.13 (dd, J = 14.0, 7.2 Hz, 1 H), 1.99 (s, 3 H), 1.69 (dd, J = 14.0, 2.8 Hz, 1 H), 1.66 (t, J = 1.6 Hz, 3 H), 1.08 (s, 3 H), 1.01 (s, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 171.3, 155.8, 122.1, 78.4, 46.9, 45.4, 27.9, 27.4, 21.6, 12.4. IR (film): 3055, 2959, 2869, 1734, 1654, 1438, 1373, 1242, 1019, 970 cm. MS: m/z (rel. abundance) = 41 (34), 43 (85), 55 (18), 67 (21), 77 (22), 91 (24), 93 (100), 108 (15), 109 (36), 111 (24), 126 (17), 153 (2), 168 (7) [M+]. HRMS (CI/CH4 on GC-MS): m/z calcd for [C10H16O2]+: 168.1150; found: 168.1151.

12

When 1.3 equiv of tert-butyldimethylsilyl chloride was used, a silicon-containing acidic byproduct was formed, which was difficult to separate from 3c. With 1.05 equiv, this byproduct was not observed.