lO.XIT.9 I ) Hydroboration of aliphatic 1-alkynes with freshly prepared dicyclohexylborane (1 mol-equiv., hexane), treatment of the resulting [(E)-1-alkenyl]boranes 5 with Et'Zn or Me,Zn (1.05 mol-equiv.) followed by addition of (-)-3-exo-(dimethylamino)isoborneol (DATB, 8; 0.01 mol-equiv.), subsequent addition of a solution of an aromatic or aliphatic aldehyde (1 mol-equiv., hexane). and quenching with aq. NH,CI provided (E)-ally1 alcohols 6 usually in 713-950/0 yield with 79-98% enantiomeric excess (Scheme 3 and Tuble).Optically pure secondmy ally1 alcohols 3b (as well as their antipodes) are key intermediates in organic synthesis. Recently, we have presented a new enantioselective approach to compounds of the type 3b based on 'asymmetrically catalyzed' additions of (l-alke-ny1)zinc reagents l a [l] and Ib [2] to aromatic and aliphatic aldehydes (Scheme I)').We now envisaged an analogous ligand-controlled 1 -alkenyl transfer from mixed (1-alkenyl)(alkyl)zinc reagents such as Ic focussing our attention on the following points: 1 ) good accessibility, 2) chemical and stereochemical stability'), 3 ) exclusive transfer of S( /lr,nlc I

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Thermal cyclizations of appropriate dienes, enynes, enones and related unsaturated systems, some of them carried out on an industrial scale, demonstrate increasingly the preparative power of the intramolecular ene reaction. A variety of substituted, fused and bridged ring systems, including natural products, are thus easily accessible in a regio-and stereo-selective manner. Numerous examples are discussed systematically illustrating the possibilities. 11 initations, and common features of this cyclization reaction and its reverse ring-opening procw Scheme 1 . The intermolecular ene reaction.Early examples of the intramolecular ene reaction (Scheme 2) date back to the 1 9 3 0~~~-" 1 ; however, its synthetic utility has become recognized only recently parallel to the general interest in intramolecular [4 + 21" '-41 and [3 + 21" 4* ' ' I cycloadditions. Similar to the cycloadditions, the intramolecular ene process profits from entropic advantage and exhibits preparatively useful regio-and stereoselectivity. This applies to three different modes of thermally-induced cyclizations (and cycloreversions) (Scheme 2) in which the enophile is linked by an appropriate bridge, either to the olefinic terminal (Type I), the central atom (Type II), or the allylic terminal (Type 111) of the ene unit. 476

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