Photochemical production processes are still extremely rare.With three examples from our own research laboratories illustration is made, how the acceptance of photochemical methodology can be increased. A diastereoselective photocyclisation and two newly designed organometallic photoinitiators succeeded because they overcome drawbacks of conventional operations.

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R 2 d -7 8 % R l T 6 a , R ' = lsobutyl ?a, R Z -Vinyl 8 a , 6 8 % (90% e e ) 8b, 59% ( 8 8 % ee j 6a, R ' = lsobutyl 6b, R ' = lsopropyl 7c, R 2 = CH, 8c, 4 6 % ( 8 3 % e e ) 7b, R Z = C,H, EH, CH, 10 (56.6%) 1 1 ( 0 . 7 % ) 12 ( 1 9 . 4 % ) 13 ( 3 . 3 % ) Scheme 2.With the chiral reagents 3 and 7a-c the enantioselective allylation of aldehydes has been achieved for the first time with organotitanium compounds. Boron reagentsI2' exhibit a similar stereoselectivity, but the advantage of titanium must not be overlooked, e.g. simple preparation, chemoselectivity, inexpensive auxiliaries, as well as the possibility of recovering diisopropylideneglucose and CpTiCI, 1. Still a drawback of this method is, however, that the high price of L-glucose impedes an equally good access to the other enantiomers of the homoally1 alcohols 4. Concerted efforts are therefore currently directed a t solving this problem with other ligands. E.uperirnen tnlStock solution of 2 in ether: A solution/suspension of 1 (11.0g. 50mmol. freshly i n Et,O (400 mL. distilled over Naihenzophenone) was treated with 26.0 g (0.1 mol) of 1.2: 5,6-di-O-isopropylidene-a-o-glucofuranose (R*OH, crystallized from cyclohexane) under argon in the absence of moisture. After 2 min at room temperature (RT) a solution of 15.2mL (ll0mmol) of Et,N in 125 m L of Et,O was added dropwise to the stirred mixture within 1 h. The resulting suspension was stirred for ca. 15 h; the Et,N. HCI was then filtered off under argon and washed three times with ca. 50 mL of Et,O (14 2 g o f E t , N . HCIvacuumdried).ThecontentofZin theyellowfiltrate(0.09 was calculated from the volume of the solution assuming a quantitative conversion. (R)-l-Phenyl-3-huten-l-ol(4a): 7.2 mL of a 1.25 M solution of allylmagnesium chloride in T H F (Aldrich, 9 mmol) was added dropwise within 10 min at O'C under argon to 110 mL of a ca. 0.09 M solution of 2 in Et,O (9.9 mmol). After stirring for 1 h at 0 C the orange suspension was cooled to -74 C and treated within 5 niin with 0.8 mL (8 mmol) of henzaldehyde. The mixture was stirred for 2 h at -74 C . warmed to ca. -3 0 ' C and hydrolyzed by addition of 16 mL of a ca. 5 M solution of H,O in T H F (1 h, RT). Filtration, washing with Et,O and drying (high vacuum) yielded 4.2 g of 5 (yellowish solid). The filtrate was evaporated and the solid residue stirred with 100 mL of hexane. Subsequent filtration furnished 4.4 g of R*OH. Chromatography (80 g silica gel, hexane: AcOEt 3.1) finally afforded 1.01 g (85%) of 4a (90% w, determined as described in (121). Received: December 21. 1Y88 [Z 3095 IE] German version:

A stereocontrolled synthetic route to optically pure (-)-(S)-ipsenol (l), the pheromone of Pityokteines curuidens and various other bark-beetle species is described. Key step of the synthesis is an enantioselective aldol reaction using a chiral titanium-cabrohydrate complex (Scheme I). The carboxylate function of the optically pure B-hydroxy acid 5 thus obtained in mol quantities is then elaborated to the dime moiety by standard methodology (Scheme 2).Various species of bark beetles are important pests to coniferous forests throughout the world. Among these are beetles of the genus Ips. In 1965 Silverstein et al.