Diastéréosélectivité de la réduction des alkyl-2 alkylidène-3 cyclopropyl alkyl cétones. Addition de RLi sur les aldéhydes α-cyclopropylidéniques

Abstract

Recu le 23 juin 19802 DOMINIQUE AUDO, MAURICE VINCENS, CLAUDE DUMONT et MICHEL VIDAL. Can. J. Chem. 59,2199Chem. 59, (1981.L'addition de RLi sur les alkyl-2 methylene-3 cyclopropane carboxaldehydes dans lesquels le groupement fonctionnel et le groupe alkyle presentent une relation trans, n'est pas diastCrtostlective alors que la reduction des (alkyl-2 alkylidkne-3 cyclopropyl) alkyl &tones presente pour certains termes une diastereoselectivite elevee qui peut atteindre la stereospecificite basse temperature. Cette selectivite depend non seulement du degre de substitution du groupe fixe sur le carbonyle mais Cgalement du radical fixe en position 2 sur le cycle mZme s'il presente une relation trans par rapport au groupement fonctionnel. Les configurationsrelatives des alcools secondaires a-cyclopropylideniques sont determinees a partir de leurs donnees en ir et rmn; ces attributions de structures s'appuient, par ailleurs, sur une filiation chimique etablie anterieurement. DOMINIQUE AUDO, MAURICE VINCENS, CLAUDE DUMONT, and MICHEL VIDAL. Can. J. Chem. 59,2199Chem. 59, (1981.Theaddition of RLi on trans 2-alkyl-3-methylene cyclopropane carboxaldehydes is not diastereoselective, while thereduction of trans (2-alkyl-3-alkylidene cyclopropyl) alkyl ketones shows for some compounds a high diastereoselectivity which may reach stereospecificity at low temperatures. This selectivity depends not only on the degree of substitution of the group fixed on the carbonyl but on the rad~cal fixed in position 2 on the ring even though it shows a trans relation with the functional group., The relative configurations of secondary a-cyclopropylidene alcohols are determined from their ir and nmr data.

Synthesis of Methylene- and Alkylidenecyclopropane Derivatives

“…Alkyl groups in alkyl-substituted cyclopropenes 257 proved acidic enough to give the isomerization in the presence of t-BuOK as the base (Scheme 96). [328][329][330][331][332][333][334] Treatment of 1-cyclopropylcyclopropene (258) with NaNH 2 led to the formation of bicyclopropylidene 14 in 30% yield. 335 Endobicyclic ACPs were formed from isomerization of bicyclic cyclopropenes.…”

“…Isomerizations of alkylcyclopropenes to ACPs is a well-documented method for the synthesis of these compounds, because, owing to a relief in ring strain, the compounds with an exocyclic double bond are thermodynamically more stable (by 6−10 kcal/mol) than those with the double bond in the endocyclic position. Alkyl groups in alkyl-substituted cyclopropenes 257 proved acidic enough to give the isomerization in the presence of t -BuOK as the base (Scheme ). −

96

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“…Cyclopropyl Grignard reagents have been obtained from the corresponding cyclopropyl bromides gem -disubstituted to the cyclopropylidene moiety and used in coupling reactions , PBr 3 , ,, Br 2 /PPh 3 , ,, I 2 /PPh 3 , (COCl) 2 . , The use of powerful oxidizing (CrO 3 /H 2 SO 4 , 4a,,,261b, CrO 3 /py, 18b,,, PCC, ,294b MnO 2 , 276e,,, NaClO 2 , NaIO 4 , 201a, oxalyl chloride/DMSO, 171b,260b,, TPAP/NMO, DDQ, H 2 O 2 , 201a,, MCPBA, 74c,g oxone, , DMDO,229c t -BuOOH 439 ) and reducing (LiAlH 4 , 4a,18b,,,,,252b,,,,,,,382a,,,, 433,437,441 NaBH 4 , , DIBAL 4a,215,252b,261b,312a,320,372,442 ) systems is generally compatible with the presence of c...…”