Addition of cuprates to chiral methyl beta-formyl carboxylates 1a-1d provided gamma-lactones 2-7 in excellent trans-selectivity. The high diastereofacial selectivity was only obtained employing diethyl ether as solvent while tetrahydrofuran gave inferior results. Similar solvent effects were observed in the additions of various Grignard reagents to 1a, which afforded gamma-lactones 2,3,12, and 13 in moderate trans-selectivity. The best solvent for these reactions was dichloromethane. The 1,3-induction of cuprate additions was studied by using aldehydes 8a-8c. The results obtained were interpreted in terms of chelate-controlled additions with formation of seven-membered ring chelates which involve both carbonyl functions of aldehyde 1 or 8. The function of ester groups as effective ligands of lithium or MgX cations may also be of importance for other stereoselective reactions employing organometallic reagents.

Neighboring‐Group Participation in the Gas Phase: Intramolecular Deacetalization of Hydroxyacetals under the Conditions of Chemical IonizationHerrn Prof. Dr. Christoph Tamm zum 70. Geburtstag gewidmet Under the conditions of chemical ionization (NH3, isobutane, ND3), hydroxyacetals do not show the expected [M + H+] signal, but the peak corresponding to the loss of the alcohol component of the acetal. This reaction is dependent on the presence of the OH group in the vicinity of the acetal and on the ring size of the heterocycle being formed. M+· is detected to a small extent as a consequence of charge exchange during chemical ionization.

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Stereoselective Synthesis von Pyrrolizidin Alkaloids from NitroalkanonesReduction of 5‐nitropentadecane‐2,8‐dione (11), synthesized by a Michael reaction from nitromethane, methyl vinyl ketone, and dec‐1‐en‐3‐one, gave, depending on the conditions, two epimeric 3‐heptyl‐2,3,5,6,7,7a‐hexahydro‐5‐methyl‐1H‐pyrrolizines as the main products: Catalytic hydrogenation (Pd/C) afforded the expected 7aα‐hydro epimer 1b with cis‐orieted H‐atoms at C(3), C(5), and C(7a). NaBH3CN/NH4OAc reduction of the nitrodione 11 yielded all four diastereoisomers with the 7aβ‐hydro epimer 1a as the predominant component; 1a is a pheromone of the cryptic thief ant Solenopsis sp. The N‐atom of the pyrrolizidine ring stems from NH4OAc exclusively as shown by reduction of 11 with NaBH3CN/(15N)H4OAc.

Depending on the conditions the reduction of 5-nitropentadecane-2,8-dione (4) gave as main products the two isomeric pyrrolizidines 1a (xenovenine, NaBH3CN/NH4OAc; as 15N-1a with NaBH3CN/15NH4OAc) and 1b (H2-Pd/C), respectively.

AbstractThe title compounds (IV) or (VIII) are prepared by ring cleavage of the methyl 2‐trimethylsiloxycyclopropanecarboxylates (III) or (VII) which are obtained either by cyclopropanation of the silyl enol ethers (I) or alkylation of the cyclopropanes (V).

A Flexible Synthesis of Methyl 4-Oxobutanoates and Their Derivatives Ring cleavage of several methyl 2-trimethylsiloxycyclopropanecarboxylates 3 provides rather sensitive methyl 4-oxobutanoates (ß-formyl esters) 4 in excellent yields. Siloxycyclopropanes 3 are easily available either directly from the corresponding silyl enol ethers 2 and methyl diazoacetate or by alkylation of deprotonated cyclopropanes 3. A highly efficient one-pot procedure affords methyl 4,4-dimethoxybutanoates 5, which can be converted into protected 4-hydroxybutanals 7 and 8 by standard methods.

The stereoselectivity of cuprate or Grignard reagent additions to chiral beta-formyl esters 1, 3, and 5 highly depends on the solvent employed. Also, the substitution pattern of the aldehyde determines whether the cis- or trans-gamma-lactone is the major product.

AbstractOn reaction with allyltrimethylsilane/TiCl4, chiral methyl β‐for‐mylcarboxylates 1a–1h provide disubstituted and tetrasubstituted γ‐lactones 3a–3h with moderate to excellent diastereoselectivities. Other Lewis acids are less selective. The formation of seven‐membered ring chelates 1 · TiCl4 has been proven unambiguously by NMR spectroscopy in several cases. Trichloromethyltitanium displays a selectivity pattern similar to the reagen combination allylsilane/TiCl4. Aldehydes 1a–1d, 1g, and 1h give primarily trans‐γ‐lactones, whereas under appropriate conditions 1f affords an excess of cis‐γ‐lactone 3f. These results are discussed with regard to the Felkin‐Anh model and to chelate formation. Model studies with simpler chiral aldehydes 5 and 7 as well as with acetals 9a/b and 11a/b are presented and discussed. They emphasize the importance of chelate control in additions to β‐formyl esters 1.