Allenic alcohols synthesis

Synthesis of allenic alcohols hy 1., 2-substitution of chlorine on ether groups by hydride... 

With the proper choice of reaction conditions, diastereoselective synthesis of a-allenic alcohols 69 and 70 from propargylic epoxide 68 was achieved [80, 81], With RMgBr and 5 mol% of CuBr/2PnBu3, anti allenic alcohols 69 are obtained with up to 100% diastereoselectivity. On the other hand, syn allenic alcohols 70 can be prepared with 88-96% diastereoselectivity with RMgCl, Me3SiCl and 5mol% CuBr (Scheme 3.36). 

The synthesis of chiral liquid-crystalline allenes was reported by Tschierske and co-workers (Scheme 4.10) [14]. An asymmetric reduction of 41 with Alpine borane was a key step to an enantioenriched allene 44. After removal of the silyl group, the allenic alcohol was etherified by the Mitsunobu method to give 45, the first liquid-crystalline allene derivatives. 

Scheme 4.26 [2,3] Wittig rearrangement for asymmetric synthesis of allenic alcohol 102.

Spino and Frechette reported the synthesis of non-racemic allenic alcohol 168 by a combination of Shi s asymmetric epoxidation of 166 and its organocopper-mediat-ed ring-opening reaction (Scheme 4.43) [74]. Reduction of the ethynyl epoxide 169 with DIBAL-H stereoselectively gave the allenic alcohol 170, which was converted to mimulaxanthin 171 (Scheme 4.44) [75] (cf. Section 18.2.2). The DIBAL-H reduction was also applied in the conversion of 173 to the allene 174, which was a synthetic intermediate for peridinine 175 (Scheme 4.45) [76], The SN2 reduction of ethynyl epoxide 176 with DIBAL-H gave 177 (Scheme 4.46) [77]. 

Scheme 4.49 Asymmetric synthesis of allenic alcohols from cyclic carbonates or sulfites...

An improved procedure for the synthesis of a-allenic alcohols in good yields and with approximately 90% e.e. was reported by Olsson and Claesson (56). (- )-(S)-3-Butyne-2-ol (25) was converted into the monotetrahydropyranyl derivatives 26a to c, which gave on reduction with LAH in ether or THF the chiral allenes 27a to c (Scheme 4). The absolute configurations of 27b and c were... 

The 36d-LAH complex has been used in the asymmetric synthesis of (3-allenic alcohols by reduction of enynols (41) as shown in eq. [14]. Although similar... 

Silver(I) catalyzed cyclizations of allenic alcohols (202) lead to 2,5-dihydrofurans (203) (79S743), whilst another mild method for the synthesis of tetrahydrofurans is the intramolecular oxymercuration-demercuration process. Geraniol, when treated with mer-cury(II) acetate and subsequently with sodium borohydride, gave a tetrahydrofuran. 

An iodine-mediated 6(0) " -exo-Trig cyclization has been used in the synthesis of (25, 4/ )-4-hydroproline from (S)-O-benzylglycidol219. Stereocontrolled 5(0) " -endo-Trig iodoetherification has provided an entry to traw.s-2.5-disubstituted tetrahydrofuran derivatives220. On treatment with iodine, trichloroimidates of primary a-allenic alcohols are converted into oxazolines with high stereoselectivity221. 

Allenic alcohols T reatment of the propargylic alcohol 1 with lithium aluminum hydride does not lead to the expected vinyl allenic alcohol 2 (3,99). However, addition of solid iodine to the intermediate aluminate does effect the desired elimination to give 2. This result was unexpected because addition of a solution of iodine in THF lends to a vinyl iodide (3). This sequence provides a general synthesis of (hydroxymcthyl)allcncs (second example). 

Deska J, Backvall J-E (2009) Enzymatic kinetic resolution of primary allenic alcohols. Application to the total synthesis and stereochemical assignment of striatisporolide A. Org Biomol Chem 7 3379-3381... 

The diacetone glucose 767 was the best reagent and has been used in the synthesis of the allenic alcohol 769 (92% de) which, after protection of the hydroxy group and final hydrolysis, afforded the unsaturated ketol derivative 770 (Scheme 199). This compound 770 is a key intermediate in the total synthesis of the cytotoxic styryl lactone (-t-)-goniodiol1051,1089. 

Homopropargylic alcohols ot-allenic alcohols. The synthesis of alkylallenes (5, 397) by the reaction of trialkylboranes and lithium chioropropargylide, ClCH2C=CLi (1), has been extended to these two systems. Thus addition of acrolein to the organoborane a can lead to either 2 or 3, depending on the temperature at which a is kept before reaction with the aldehyde (equation I). If the aldehyde is... 

Pomet, J., Randrianoelina, B. Action of 1-trimethylsilyl-2-butyne on carbonyl derivatives in the presence of catalysts synthesis of a-allenic alcohols or chloroprenic derivatives. Tetrahedron Lett. 1981,22, 1327-1328. 

Allenic alcohols.3 The reaction of allylsilanes with carbonyl compounds catalyzed by this salt to give homoallylic alcohols (9, 455-446) has been extended to a synthesis of a-allenic alcohols. Use of TiCl4 as catalyst results in a 2-chloro-l,3-diene. 

Several interesting approaches to the synthesis of /I-ketophosphonates have recently been described. Typically, standard Arbuzov synthesis of /1-ketophospho-nates is unsatisfactory due to a competing Perkow reaction [51]. However, y,d-unsaturated /1-ketophosphonates are obtained in high yield via Arbuzov reaction of triethyl phosphite with a-iodoenones, readily available from tertiary allenic alcohols [52]. Another successful example of an Arbuzov-based approach involves reaction of bromoacetylated polystyrene with triethyl phosphite, which provided immobilized /J-ketophosphonate in excellent yield [53]. In another approach, the lithio derivative of dimethyl methylphosphonate was reacted with Weinreb amide to obtain the corresponding /J-ketophosphonate [54]. a,a-Diflu-oro-a-ketophosphonates have been synthesized via a cerium-mediated route... 

The vinylallene 110, derived from dibenzobarrelene, has been used as a precursor for penta-1,2,3,4-tetraene. An improved synthesis of 110 started with the conjugated dibromocyclopropyl ketone. Treatment of the ketone with excess methyllithium gave the desired compound 110 after treatment with alumina. Presumably the allene alcohol is involved in this series of reactions. ... 

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