2-Lithio-2- tetrahydropyran

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. 

Hydroxyl-terminated polymers have also been prepared 337 338) using organo-lithium initiators with protected hydroxyl functionality. Thus, using initiators such as 2-(6-lithio-n-hexoxy)tetrahydropyran (A) and ethyl 6-lithiohexyl acetaldehyde acetal (B), it was... 

Lactols and their acetals can be transformed easily into their 2-arylsulfonyl derivatives 337 by reaction with a sulfinic acid under Lewis acid activation. The corresponding organolithiums are prepared by deprotonation with n-BuLi or LDA and, after reaction with electrophiles, a /(-elimination of sulfinic acid afforded a cyclic a-substituted enol ether514,547,548. 2-Lithio-2-(arylsulfonyl)tetrahydropyrans equilibrated to give mainly the anomer with the lithium atom at the equatorial position549. 

Ley and coworkers have found that dispiroketals383, such as 1,8,13,16-tetrahydro-oxadispiro[5.0.5.4] hexadecanes, show a wide range of synthetic applications554. For the preparation of these compounds, 2-(tri-n-butylstannyl)dihydropyrans can be used554-556. The reaction of 2-lithio-6-methyl-2-(phenylsulfanyl)tetrahydropyran (375) with tri-n-butylstannyl chloride gave compound 381, which has further been transformed into the dispiroketal 382 (Scheme 100)555. 

Lithio-l-(tetrahydropyran-2-yI)-lH-pyrazoI (Losung)1866 Zu einer Losung von 2,0 g (8,7 mmol) 4-Brom-... 

Convenient access to a broad array of related reagents in a predictable manner. Certainly, the deprotonation of a simple precursor by strong commercially available bases, such as alkyllithium reagents, is the first choice (see Sects. 2.4-2.S). Reductive Uthiations are also useful, particularly in the dias-tereoselective generation of 2-Uthio-tetrahydropyrans and 2-lithio-13-diox-anes (Sect. 2.1). 

Cl 1-25 of the milbemycins. The intramolecular spiroketalization theme was slightly altered to feature an endocyclic enol ether [86] by condensation of a lithio-2-benzenesulfonyl-tetrahydropyran with a suitable epoxide. An alternative but not enantiospecific approach from lactone B 3 comes from a double Baeyer-Villiger oxidation of bicyclo[2.2.1]heptane-2,5-dione to control [107] the relative stereochemistry in the B ring. The acetylenic partner was in turn derived from two different routes, the more selective being an anti hydroxyl group directed alkylation of a homopropargylic alcohol. 

A "cascade" reaction, the preparation of isobutyric acid dianion, was achieved by a one-pot sequence, the formation of butyllithium, deprotonation of di-i-propyl amine to LDA, then formation of the acid dianion. Quenching with benzal-dehyde gives the hydroxyacid in 78% yield. 2-Lithio-furan and -anisole were prepared and used in several synthetic reactions. some instances, it can be advantageous to replace THF by tetrahydropyran (THP), a solvent with a better stability in the presence of strong bases. 

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