a-Heterosubstituted allylboronates 7 are prepared. Addition of 7 to aldehydes results in E/Z-isomeric hornoallyl alcohols 13 and 14: The reasons for the predominant formation of the Z-isomer 14 are discussed. The Z-bromo olefins 16 and 20 obtained in this way serve as starting point for chain extension or formation of &lactones 21. Many allyl metal compounds add to aldehydes and ketones with "allyl inversion" *). Those allyl metal compounds having a n a-alkyl branch should therefore lead to adducts 1 with a linear alkene chain. Accordingly, this reaction ought to be useful for assembling larger alkyl chains". The same target could be reached by using a-heterosubstituted allyl metal compounds, which can be considered as multicoupling building blocks 34), because in the resulting adducts 2 the heteroatom can be substituted by an alkyl chain using either the cuprate-') or the NiO-@ and Pdo7)-catalyzed carbon carbon bond forming reactions. Stereoselektive Synthese von -Met 4-y"Of course, such methodology requires that structurally defined q '-ally1 metal compounds are existant and available. Yet these compounds appear to be exceptional in view of the generally fluctional nature of the allyl compounds of electropositive metals.

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Das Aziridin-Derivat 9 wird bei der Dichlorcarben-Addition, der Hydroborierung und der Hydrierung etwas mehr von der syn-als von der anti-Seite her angegriffen. Wahrend bei 9 keine nennenswerte Wechselwirkung zwischen Dreiring und semicyclischer Doppelbindung besteht, laBt sich eine deutliche Orbital-Wechselwirkung bei den Cyclopropan-Derivaten 6 und 7 nachweisen. Dies wird mit einem bevorzugten anti-Angriff der genannten Reagenzien auf die Doppelbindung in 6 und 7 in Zusammenhang gebracht. Bicyclofulvenes, IX Stereoelectronic Effects in Additions to 8-Methylenetricycl0[3.2.1.O~~~]octane DerivativesAddition of dichlorocarbene to the double bond of the aziridine derivative 9 as well as hydroboration or hydrogenation proceed with a slight syn preference. Whereas 9 lacks significant interaction between the three-membered ring and the semicyclic double bond, interaction is marked in the cyclopropane derivatives 6 and 7. This is considered to cause the preferred anti-attack by the above mentioned reagents.Oberseite und Unterseite einer Doppelbindung sind nur bei solchen Olefinen gleich, in denen die Ebene der Doppelbindung eine Symmetrieebene des Molekiils ist, wie z. B. bei 1. Bei anderen Olefinen kann die Storung, die zu einer Ungleichheit der Ober-und Unterseite fiihrt, sterische und elektronische Ursachen haben: So liegt z. B. in 2') eine einseitige elektronische und sterische Wechselwirkung vor.DaL3 die Doppelbindung in 2 von Elektrophilen anti zum Aryl-Rest angegriffen wird, ergibt sich damit allein schon aus sterischen Griinden. Um den EinfluD elektro-

The preparation of the (u-chloroally1)boronate 4 of 92% e.e. is described. Its addition to achiral aldehydes resulted in the homoallyl alcohols 6 of 82-92% e.e. Cooperative diastereoface selectivity on addition of ent-4 to isopropylideoeglyceraldehyde (22) gave the product 23 of high diastereomeric purity. Reagent control of stereoselectivity on addition of 4 to 22 resulted in 25 of 77% diastereomeric purity. Stere-lektive Synthese von Alkoholen, XXIII ') Chkalitiitsiibertragung bei der Addition von (a-Chlorallyl)boronsiureestern an AldehydeDie Darstellung des (a-Chlorally1)boronslureesters 4 mit 92% e.e. wird beschrieben. Seine Addition an achirale Aldehyde ergab die Homoallylalkohole 6 mit 82-92% e.e. Bei der Addition von ent-4 an Isopropylidenglycerinaldehyd (22) fiihrte die kooperative Diastereoseitendifferenzierung zum Produkt 23 hoher Diastereomerenreinheit. In der Reaktion von 4 mit 22 ergab die Stereokontrolle durch das Reagenz den Alkohol25 mit einer Diastereomerenreinheit von 77%.In the field of asymmetric syntheses the addition of chiral organometallic reagents to aldehydes and prochiral ketones has been under active investigation during the last decade2). Typical examples for such reagents are the allylboron compounds 1 having chiral residues on boron 3,4). Their addition to aldehydes leads to the homoallyl alcohols 3, a reaction in which the extent of asymmetric induction has been constantly improved, now frequently reaching and in some cases exceeding the 90% e.e. level9.The addition of the allylboron compounds 1 to aldehydes proceeds via cyclic six-membered transition states 2. In the reactions mentioned above asymmetric induction resulted from chiral control elements which were affixed to the periphery 0 VCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1986

In a pair of diastereomeric ß‐hydroxy ethers the relative 1H‐NMR chemical shift of the OH proton is diagnostic for the syn or anti stereostructure. This is probably based on the presence of internally hydrogen‐bonded structures. The rule is therefore restricted to those compounds for which only this type of internal hydrogen bonding is accessible.