Ammonium salts, alkyl isomers

The preparation of conjugated dienes from pyridines is exemplified by the transformation of 2-picoline into the sex pheromone (669) of Lobesia botrana, a major pest of vineyards (Scheme 154) (80TL67). Thus, the lithio salt of 2-picoline was alkylated by 2-(5-chloropentyl-oxy)tetrahydropyran, the resulting pyridine (665) N-methylated, and the pyridinium salt reduced by sodium borohydride. Quaternization of the 1,2,3,6-tetrahydropyridine (666) and Hofmann elimination gave the (7 , 9Z)-undecadien-l-ol (667) as the sole isomer. Protection of the alcohol and treatment of the corresponding ammonium salt (668) of the amine with lithium dimethylcuprate gave pure (669) after hydrolysis, acetylation and HPLC purification. 

Alkylation of 1-vinyl tetrahydroisoquinoline with ethyl bromoacetate afforded the ammonium salt in high yield (Equation 43). Treatment of this compound with DBU in THF at room temperature gave the [2,3]-sigmatropic rearrangement product 305 in 70% yield. The product consisted of a mixture of isomers in an (E)/(Z)-ratio of 96 4 <2005JOC5519>. 

More recently/157) dextromethorphan and levomethorphan have been resolved via their respective quaternary ammonium salts with n-alkyl iodides. The ratio of axial and equatorial isomers produced during quaternization with Me, n-Pr, and n-Bu iodides was assessed by H- and 13C-nmr. 

C (rCi3 LAS determination of alkyl chain length distribution isomer separation trace analysis Reaction of the tetrabutyl-ammonium salt in the hot injection port to form the butyl ester of LAS J W DB-5MS 5% phenyl dimethylsilicone, 0.25 mm x 30 m, 0.25 urn film 3 min hold at lOO - C, then to300 at7sC/min Ion trap MS 123 ... 

---