Durch Reduktion von Benzvalen (1) mit Diimin wird das Tricyclo[3.1.0.0~~6]hexan (3) in guter Ausbeute erhalten. Das Verfahren macht das bereits von Lemal und Shim dargestellte 3 erheblich leichter und in groBeren Mengen zuganglich. 1H-und 13C-NMR-spektroskopische Daten werden diskutiert. Sowohl die thermische als auch die AgBF4-katalysierte Umlagerung von 3 fuhrt zu 1,3-Cyclohexadien (8). -Die Ozonolyse von 1 mit anschlieBender LiAIH4-Reduktion ergibt das cis-l,3-Bis(hydroxymethyl)cyclobutan (13a). Diimine Reduction and Ozonolysis of BenzvaleneVia reduction of benzvalene (1) with diimine tricyclo[3.1.0.02~6]hexane is obtained in good yield. The procedure renders 3, which has already been synthesized by Lemal and Shim, accessible much easier and in larger quantities. * H and 13C n.m.r. spectroscopic data are discussed. Both the thermal and the AgBF4-catalyzed rearrangement of 3 yield 1,3-cyclohexadiene (8). -The ozonolysis of 1 with subsequent LiAlH4-reduction results in cis-1,3bis(hydroxymethy1)cyclobutane (13a).

Unter kinetisch kontrollierten Bedingungen ( -50 "C, 10 min) vereinigten sich die Carbonsiiuredianionen 2 mit Aldehyden 3 zu den threo/erythro-Addukten 4/5 (Schema I), wobei der threoAnteil mit der Raumerfiillung der Substituenten an 2 oder 3 stark ansteigt und mit dem Ladung/Radius-Verhaltnis der zu 2 gehorigen Gegenionen ebenso deutlich abfallt. Daraus wird auf einen syn-Ubergangszustand mit cycloadditionsahnlicher HOMO-LUMO-Wechselwirkung zwischen 2 und 3 geschlossen (Schema 3). Unter thermodynamischer Kontrolle (22-50°C, 1 -3 Tage) erhoht sich bei geeigneter Substitution die threo-Selektivitat gegeniiber der kinetischen Kontrolle betrachtlich. Es wird die Reindarstellung der aus 4 und 5 durch saure Hydrolyse entstehenden Hydroxysauren 6 und 7 beschrieben, deren Konfiguration auf Grund von 'H-NMR-Daten zweifelsfrei zugeordnet werden kann. Stereochemistry of the Addition of Carboxylic Acid Dianions to Aldehydes under Kinetic andThermodynamic Control -Synthesis and Configurational Assignment of 2,3-Disubstituted threo-and erythro-3-Hydroxycarboxylic AcidsUnder kinetically controlled conditions ( -50"C, 10 min) the carboxylic dianions 2 add to aldehydes 3 to give the threo/erythro-adducts 4/5 (Scheme 1); the threo-selectivity markedly increases with the bulkiness of the substituents of 2 or 3 and decreases with the charge/radius ratio of the counter-ions of 2. From these results a syn-transition state with a HOMO-LUMO interaction between 2 and 3 is derived (Scheme 3). For appropriate substituents a far higher threo-selectivity is observed under thermodynamically (22 -50 "C, 1 -3 days) than under kinetically controlled conditions. We describe the isolation of the hydroxy acids 6 and 7, which are formed from 4 and 5 on acidic hydrolysis, and show how their configurations can be unambiguously assigned on the basis of 'H-NMR data.Seit den klassischen Arbeiten von House') und Rathke') ist die Addition ,,vorgeformter" (performed) Enolatsysteme an Carbonylverbindungen zu einem Schwerpunkt organischchemischer Forschung geworden3). Vor allem die Stereochemie beziiglich der neu gekniipften C -C-Einfachbindung -d. h. also die bevorzugte Bildung des threooder erythro-Isomeren -hat in letzter Zeit, vor allem im Hinblick auf naturstoffsyn-7 Korrespondenz bitte an diesen Autor richten.

Szcmmary threo-3-Hydroxycarboxylic acids, which are enol ethers with the triphenylphosphinediethyl azostereoselectively obtained from metallated carboxylic dicarboxylate-adduct, whereas the corresponding (E)acids and aldehydes, are converted into (, %' )-ol efi ns and isomers are prepared via the p-lactones.

The question of hydroxy group activation (HGA) us. carboxy group activation (CGA) always arises when dehydrating agents react with hydroxy carboxylic acids; this problem is of particular importance in the synthesis of macrolides['l (stereocontrol['' of a chiral center at the lactone-0) and pep-tided3] (problem of hydroxy protection on preparing the active ester derivatives of hydroxyamino acids). It has generally remained unclear so far whether a given dehydrating agent exclusively effects HGA or CGA, or whether a variation of the substituents in the substrate may lead to a change in the activation mode.In the case of the adduct (1) of triphenylphosphane and diethyl azodicarboxylate, a frequently employed dehydrating agentr4], only HGA was known in the system alcohol-carboxylic acidL5'. We now report on the first CGA reactions of (1) and reveal the factors determining the HGA/CGA competition.As can been seen from the formula scheme our model system-the reaction of ( I ) with threo-3-hydroxycarboxylic acids (2)[61-allows a simple and unambiguous differentiation between CGA and HGA. Proton transfer generates the ion pair (3), from which the zwitterions (A) or (B) are formed by elimination of hydrazo ester. Of the reaction products, (4) and (5) can be unequivocally assigned to (A), while (6) can only be formed from (B); the alternative (B)-+(7)+ (8) is about 30 kcal/mol['I less favorable and can be ruled out. The ratio HGA/CGA can thus be expressed by the quotient Q= ~4 ) 1 + [(.VI/[(~A able 1).The relationship between Q and R'/R' is attributed to the fact that the energy levels of (A) and (B) are shifted relatively to each other under steric effects. For small R ' and R' (A) is much more stable than (B) due to the high resonance energy of its carboxylate function; so exclusively HGA is observed in cases (a)-(e). On the other hand, bulky R ' and R2 in (A) strongly interact with each other and the P(ChH5)3 group, whereas the steric interference is far less in (B); hence, in the systems (/)-(

ET ["I and 815f.61 the refractive index n and its functions yield the best correlations, saving the tetrachloromethane values. With ( 1 -l/n2), the solvent-dependent term of an energy parameter'5'', one obtains the relationships (10) to (12) (valid at 20 "C): -Karlstr. 23,