ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
2-Stannyl-1,3-dithianes. Preparation, Sn/Li-Transmetallation, and Use for CyclizationsIn order to test the possibility of generating nucleophilic 2-lithio-1, 3-dithiane centers in the presence of electrophilic groups in the same molecule, the stannylated dithianes 1-3 were prepared or generated. Solutions of the lithio derivatives 2a and 2b could either be obtained by metallation of 1 with lithiumdiisopropylamide (LDA) or by transmetallation of 3 with alkyllithium reagents. Alkylations of 2 led to the alkyl-stannyl-dithianes 4-7. Additions of the trimethylstannylated lithiodithiane 2a to aldehydes and ketones at low temperature led - after hydrolysis - to the adduct alcohols 8; warming up to room temperature before hydrolysis furnished keten thioacetals 9 only with acetone (→ 9b) and cyclohexanone (→ 9c) as carbonyl component, while still the simple adducts 8a and 8d were isolated with benzaldehyde and cyclohexenone, respectively. Methyl benzoate and benzoic acid anhydride reacted with 2a to produce the tin-free derivatives 12 and 14, respectively.It is shown that the Sn/Li-exchange at the 2-position of dithianes 4-7, 15 and 16 takes place within minutes at -78°, whereas H/Li-metallation does not occur at all at this temperature. In situ preparation of the cyclization products 17-19 from halo-epoxides is described. The overall yields of Sn/Li-exchange (3 → 2), epoxyalkylation (2 → 15 and 16, repectively), Sn/Li-exchange in 15and 16, cyclization (→ 17-19) are twice as high (up to 80%) with the tributylin than with the trimethyltin derivatives. The intramolecular 1, 3 nucleophilic reaction 20a → 17 is complete within 5 min at -78°. The total yields of cyclization products by the tin route (3b → 16 → 20b → 18 + 19) and by direct metallation (1, 3-dithiane →21b → 20b → 18 + 19) are 63 and 30%, respectively.
Additional Material:
2 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19780610722
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