A study of the pressure‐dependence of the title reaction (up to 7 kbar) yielded valuable conclusions about its reaction mechanism. The likewise expected product erythro‐4 was not observed.

Angm (%em. In!. Ed. Engl. 29 (1990J No. 6 c> YCH Yerlagsgesrllsrhafi mbH. 0.6940 Wernheim. 1990 oS70-0H33j90]0n06-0675 $03.SO+ .25/0 675

Geminal Substituent Effects, 4. — The Dependence of the Inverse Anomeric Effect of Geminal Cyano Groups on the Structure The heats of combustion and the heats of sublimation of malodinitrile (1a), ä‐alkyl‐ (1b,c) and å, å‐dialkylmalodinitriles (1 d ‐f) have been determined. From the obtained standard heats of formation group increments for CH2[CN]2], CH[(CN)2 Cl and C[CN)2C2] group are deduced. The comparison of their values with corresponding increments for monocyano alkanes reveals a synergetic destabilisation by two geminal cyano substituents of 11.5, 9.0 and 6.6 kcal/mol, respectively. Thus, this inverse anomeric effect decreases by increasing alkyl substitution.

The (R,S)-aminal 3 , prepared from glycine methyl ester hydrochloride, methylamine, and pivalaldehyde,l'"l was treated with 14 chiral carboxylic or sulfonic acids. In two cases one of the two possible diastereomeric salts crystallized selectively: the salt from ( -)-2,3 :4,6-di-O-isopropylidene-2-ketogulonic acid [( -)-diacetone-2-ketogulonic acid] and ( S ) -3 , and that from (S)-( -)-mandelic acid and ( R ) -3 . For preparative resolution a single crystallization with mandelic acid gave enough enrichment so that N-benzoylation and recrystallization of 2 produced the two enantiomers with greater than 98% ee. Mandelic acid is recovered in 95% yield without detectable racemization.I "] This work was supported by the Minister fur Wissenschaft und Forschung des Landes Nordrhein-Westfalen and by the Fond der Chemischen Industrie. We thank Prof. Dr. H Duddeck and Dr. M . Kaiser. Universitat Bochum, for the recording of the high-resolution NMR spectra and the help with their interpretation. 346 0 VCH Verlagsgesellschaft mbH. 0-6940 Wernherm. 1986

Dem anomeren Effekt geminaler Donorsubstituenten sollte ein inverser Effekt geminaler Acceptorsubstituenten entsprechen. Dies konnte für die Ester 1 und 2 durch Ableitung von Gruppeninkrementen bestätigt werden: Die Diester werden um ca. 3 kcal mol‐1 gegenüber Monoestern und der Triester wird um ca. 6 kcal mol‐1 gegenüber Diestern destabilisiert. Die Reaktivität dieser Verbindungen (z. B. ihre Acidität) erscheint mit diesem Befund in einem neuen Licht (R = H, Me).