Syntheses of Phencyclone Analogues. Applications for NMR Studies of Hindered Rotations and Magnetic Anisotropy in Crowded Diels

TCE

The Chemical Educator

ISSN: 1430-4171 (electronic version)

Table of Contents

Abstract Volume 6 Issue 4 (2001) pp 227-234

Syntheses of Phencyclone Analogues. Applications for NMR Studies of Hindered Rotations and Magnetic Anisotropy in Crowded Diels–Alder Adducts

Ronald Callahan,^†^† Kimberly Marshall,^† Robert Rothchild,^*,† and Kerstin Rosmarion^†

^†John Jay College of Criminal Justice, City University of New York, Science Department, 445 West 59th Street, New York, NY 10019-1128, rrothchild@jjay.cuny.edu; and ^††Chemistry Department, New York University, 569 Brown, 29 Washington Place, New York, NY 10003
Received January 25, 2001. Accepted March 1, 2001

Published online: 22 June 2001

Abstract. Undergraduate organic chemistry special laboratory projects based upon the synthesis of phencyclone, 1 (a potent Diels–Alder diene), and the preparation of a series of highly hindered Diels–Alder adducts of the phencyclone, were described earlier. Details of the synthesis of an analogue of 1 are presented here as an extension of these projects. The analogue, 3,6-dibromophencyclone, 2, and adducts from a wide range of dienophiles, can be prepared by undergraduate organic chemistry students. These adducts (from 1 or 2) are eminently suitable for student characterization by NMR to examine aspects of hindered rotation, magnetic anisotropy, and dynamic NMR spectroscopy, using modern one- and two-dimensional multinuclear methods with a medium-field instrument (7 T), to observe ¹H, ¹³C, and ¹⁹F. Use of 2 effectively doubles the range of potential target compounds for students. The Diels–Alder adducts (and their precursors) have been studied by molecular modeling methods. This present paper describes the reaction of 2 with 4, the dienophile N-(4-dimethylamino-3,5-dinitrophenyl)maleimide (“Tuppy’s maleimide”), to form the adduct 5. Compound 5 has been well-characterized by ¹D and ²D ¹H and ¹³C NMR, and is illustrative of the wide range of adducts that can be made from 2 by students. The structure of 5, as determined by geometry optimization at the semiempirical (AM-1) level, is included here.

Key Words: Laboratories and Demonstrations; organic chemistry; 2-D NMR; multinuclear

(*) Corresponding author. (E-mail: rrothchild@jjay.cuny.edu)

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