Electropositive elements are prerequisites for the formation of anti van't Hoff/Le Bel geometries, as evident in compounds 1, which contain planar tetracoordinate boron atoms in the CB2H framework. These compounds extend the range of molecules of this structural type to include those without metal atoms. R = CH(SiMe3)2, R′ = 2,3,5,6‐Me4C6H.

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7] a) Programm DMol V2.3 der Biosym Technologies Inc. Es wurden doppelte numerische Basissdtze rnit Pobarisationsfunktionen verwendet ; die inneren Orbitale wurden nicht explizit berucksichtigt (frozen core). Die Vosko-Wilk-Nusdir-Korrelationsfunktion [7 b] und die Becke-Austauschfunktion [7c] rnit nichtlokalen Korrekturen wurden eingesetzt. Rechnungen fur die Anionen mit einer gerdden Zahl von negativen Ladungen wurden ,,spin restricted", d. h. rnit gleichen Orbitalen fur Elektronen rnit a-und [&Spin, durchgefuhrt; die Struktur wurde ohne Geometriebeschrankung optimiert. Die elektronischen Strukturen und Details zu den Geometrien werden in einer ausfuhrlichen Originalmitteilung veroffentlicht werden. b) S. [9] Partialladungen der Atome fur [M,,(CN),J: Zn + 0.59. Cd + 0.69; C,,,, -0.21 (Zn), -0.24 (Cd); N,.,, -0.14 (Zn), -0.15 (Cd); CB,, -0.18 (Zn), -0.21 (Cd); N,, -0.10 (Zn), -0.11 (Cd); Dielektrizitatskonstante = r ; quadratische Winkelkonstanten (kJ rad-* mol-') C-M-C 125, C-M-N 125, M-C-N 209, M-N-C 209; Parameter der Potentialmulde fur nichtbindende Wechselwirkungen r* [A]. E* [kJmol-'] 2.03,0.63 (C); 1.96,0.71 (N); 1.90.0.62 (Zn); 2.30, 0.96 (Cd); Berechnungen rnit Discover V2.9

SiMe, 43 1 OC0,Et OC02Et 26 Me3si3 25 sented here proceeds along path b, and not along path a (Scheme 1). The alkenyltitanium intermediate of type C (Scheme 1, ML, = Ti(OiPr),) can be trapped by iodine in excellent yield (Table 1, entry 7). This intermediate reacted with an aldehyde to give the adduct in high yield (entries 8 , 11-13), thus allowing the extension of the side chain after the cyclization by a n onepot procedure (Scheme 3 ) . Scheme 3 Trapping with an aldehyde of the intermediate obtained from 1 and the 2.7-enynyl carbonate 7.The sequence of cyclization followed by trapping with an aldehyde has been widely utilized in the case of lithium-and magnesium-ene reactions for synthesis of polysubstituted cycloalkanes and corresponding natural products.[*"] The present reaction, which can be regarded as synthetically equivalent, at least in part. to these intramolecular metallo-ene reactions, should also find wide applicability in organic synthesis. Moreover, several functionalities that are labile under the reaction conditions for the magnesium-and lithium-ene reactions are not attacked by the titanium compounds (see Table 1, entries 12 and 13). Thus, the present reaction could offer an even wider range of possibilities, which we are currently investigating. E.xperirnentu1 SectionTypical procedure (synthesis of 20, Table 1, entry 11): To a solution of 9 (0.082 g, 0.308 mmol) and [Ti(OiPr),] (0 113 mL, 0.385 mmol) in ether (3.0 mL) was added rPrMgCl(0.65 mL. 1.13~inether.0.739 mmo1)at -5O"C,and thereactionmixture was subsequently allowed to warm to room temperature. After the reaction mixture had been stirred for I h. propanal (0.033 mL, 0.462 mmol) was added, and the mixture was stirred for a further hour. Aqueous workup (1 N HCI) and column chromatography (silica gel. hexane8AcOEt 30,'l) provided 20 (0.054 g, 74% yield) as a 58.42 mixture of diastereoisomers. ' H N M R (300 MHz. CDCI,): major diastereoisomer ii = 0.74-0.89(m.6H). 1 17-1.64(m, 12H).1.65-1.79(rn, l H ) , 1.82-2.08 (m. 2H). 2 11-2.34 (m, 2H), 3.26-3.36 (m, l H ) , 4.27-4.36 (m. l H ) , 4 89-4.96 (m. I H). 5.80 (ddd, J = 17.0, 10.2.6.82 Hz, 1 H); minor diastereoisomer: 6=0.74-089 (m. 6 H ) .