2-Lithio-l ,3-dioxolane

L. Colombo, M. Di Giacomo, G. Brusotti, and G. Delogu, Chiral 2-lithio-l,3-dioxolanes and 2-lithiooxazolidines New formyl anion equivalents. Tetrahedron Lett. 35 2063 (1994). 

Dialkoxymethyllithiums 43 3649 and 434649 651, 2-lithio-l,3-dioxolane 435649 and 2-lithio-1,3-dioxane 436649 are formyl anion equivalents, which have been prepared either by reductive lithiation of 2-(phenylsulfanyl) substituted precursors at —95 °C649 or by trans-metallation of 2-(tri-n-butylstannyl) substituted compounds at —110649 or —78°C651. The starting acyclic phenylsulfanyl precursors can be prepared from the corresponding orthoformates by reaction with (phenylsulfanyl)trimethylsilane and trimethylsilyl triflate as catalyst (for compounds 433 and 434). The cyclic derivatives (435, 436) were prepared from l,2-bis(l,3-dioxolan-2-yloxy)ethane and propane, in the same way649. 

The addition of 2-lithio-l,3-dioxolane (435) to the thionolactone 441, followed by quenching with 1,4-diiodobutane, afforded the diene 442 in 68% yield, the postulated mechanism being shown in Scheme 116653. The oxanonacene prepared is a unit of breve-toxine A. 

Enantiopure 2-stannyl-l,3-dioxolanes derived from chiral diols have been transmetal-lated to give chiral 2-lithio-l,3-dioxolanes 443 and 444 but, after addition to aldehydes, very low diastereomeric ratios were obtained654. 

Alkylation of a-lithio-iV,/V-dimethylhydrazones with 2-(iodomethyl)-l,3-dioxolane provides masked 7-hydrazonoaldehydes. Cyclization occurs after acid-catalyzed removal of the dioxolane protecting group and the /V-unsubstituted pyrrole can be obtained by hydrogenolysis of the N,N-dimethylamino substituent (Scheme 41) (88JHC1135). 

Silyl, germanyl and stannyl alk-l-ynyl ketones have been prepared from 2-lithio-2-(trimethylsilylethynyl)-l,3-dioxolane 448. The deprotonation of the dioxane 447 with n-BuLi at — 65 °C afforded the acyl anion 448 which, after reaction with trimethylsilyl, trimethylgermanyl and trimethylstannyl chloride, gave the expected derivatives (Scheme 117)658. Hydrolysis of these products with 0.01 M sulfuric acid at room temperature in aqueous acetone gave the corresponding acyl derivatives 449. On the other hand, the reaction of the intermediate 448 with alkyl halides allows the synthesis of acetylenic ketones659. 

Related Reagents. (4a/ )-(4aa,7a,8a/3)-Hexahydro-4,4,7-trimethyl-4//-l,3-benzoxathiin 2-Lithio-l,3-dithiane 1,1,3,3-Tetramethylbutyl Isocyanide Benzothiazole Bis(phenylthio)-methane Af,Af-Diethylaminoacetonitrile Diethyl Morpholino-methylphosphonate 1,3-Dithiane 2-(2,6-Dimethylpiperidino) acetonitrile Cyanotrimethylsilane Samarium(II)iodide-l,3-dioxolane (Phenylthiomethyl)trimethylsilane. 

Thiophen Analogues of Isoquinoline.—4,7-Dimethylthieno[2,3-c]pyridine has been synthesized by hydrolysing the acetal function of (252). This compound was obtained by the reaction of 2-(3-lithio-2-thienyl)-l,3-dioxolan with diacetyl followed by oximation and reduction. 6,7-Dimethylthieno[3,2-c]pyridine was obtained in an analogous manner, (2,5-Dimethyl-3-thienyl)acetone gave (253) on acylation. Treatment with perchloric acid gave the pyrylium salt (254), which upon reaction with NH3 gave (255). The same reaction sequence with (3-benzo-... 

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