Allyl alcohols acyclic

The Asymmetric Cyclopropanantion of Acyclic Allylic Alcohols Efficient Stereocontrol with lodomethylzinc Reagents," Charette. A.B. Marcoux, J.-F. Synlett, 1995, 1197... 

In the case of acyclic allylic alcohols, an efficient kinetic resolution of l-buten-3-ol was achieved using [Ru((7 )-BINAP)(H)(CH3CN)(THF)2]BF4 as catalyst (Equation (16)).55... 

Related catalytic enantioselective processes It is worthy of note that the powerful Ti-catalyzed asymmetric epoxidation procedure of Sharpless [27] is often used in the preparation of optically pure acyclic allylic alcohols through the catalytic kinetic resolution of easily accessible racemic mixtures [28]. When the catalytic epoxidation is applied to cyclic allylic substrates, reaction rates are retarded and lower levels of enantioselectivity are observed. Ru-catalyzed asymmetric hydrogenation has been employed by Noyori to effect the resolution of five- and six-membered allylic carbinols [29] in this instance, as with the Ti-catalyzed procedure, the presence of an unprotected hydroxyl function is required. Perhaps the most efficient general procedure for the enantioselective synthesis of this class of cyclic allylic ethers is that recently developed by Trost and co-workers, involving Pd-catalyzed asymmetric additions of alkoxides to allylic esters [30]. 

Cyclopropanation.1 The carbenoid obtained from the reaction of CH2I2 with Sm or Sm/Hg in THF effects cyclopropanation of ally lie alcohols, but not of isolated double bonds. The reaction of both cyclic and acyclic allylic alcohols proceeds in generally high yield and often with marked diastereoselectivity. 

In the epoxidation of acyclic allylic alcohols (Scheme 6), the diastereoselectivity depends significantly on the substitution pattern of the substrate. The control of the threo selectivity is subject to the hydroxyl-group directivity, in which conformational preference on account of the steric interactions and the hydrogen bonding between the dioxirane oxygen atoms and the hydroxy functionality of the allylic substrate steer the favored 7r-facial... 

One of the classical ways to perform diastereoselective 1,3-dipolar cycloaddition is by the addition of a 1,3-dipole to an allyl alcohol derivative (65, 107-120). Very recently, a short review article was devoted to this area (13). Among the most commonly applied acyclic allyl alcohol derivatives are alkenes 73-75 (Scheme 12.25). These alkenes have been used in reactions with nitrones. 

For secondary acyclic allylic alcohol benzoates, resolved by Sharpless enantioselective epoxida-tion, there is a similar relation between the sign of the benzoate Cotton effect and absolute configuration, as in 7 and 8149. 

Scheme 2.1.4.11 Synthesis of enantiopure cyclic and acyclic allylic alcohols.

The diastereoselective cyclopropanation of acyclic allylic alcohols is a very useful synthetic transformation. It was recognized early on by Pereyre and coworkers that the cyclopropanation of Z-substituted chiral allylic alcohol was highly syn selective (equation 58) °. It was later shown that most zinc carbenoids react with these substrates with high syn stereocontrol. 

The model involving the minimization of the A-1,3 ally lie strain followed by an alkoxy-directed cyclopropanation is quite reliable to predict the sense of induction in the cyclopropanation of chiral acyclic allylic alcohols. However, the application of this model is not as straightforward in the case of allylic ethers. Indeed, it was shown that the cyclopropanation of benzyl ethers led to a major anti or syn isomer depending upon the nature of the substituents (equation 67). ... 

Allylic and cis-homoallylic alcohols are epoxidized readily, but frans-homoallylic and bishomoallylic alcohols react slowly, if at all. The stereoselectivity in the epoxidation of acyclic allylic alcohols is the same as and is comparable to that observed with r-BuOOH/VO(acac)2. The stereoselectivity in epoxidation of acyclic homoallylic alcohols is also the same but lower than that obtained with t-BuOOH/ VO(acac)2. Epoxidation of cyclic allylic alcohols proceeds more slowly and in lower yield than that of acyclic allylic alcohols. 

Cyclizations of chloral hemiacetal derivatives of cyclic allyl alcohols were regio- and stereo-selective (Table 6, entry 1), but a mixture of regioisomers was obtained from analogous derivatives of acyclic allyl alcohols with a nonterminal double bond.93 Hemiacetal derivatives of allyl alcohols with a terminal vinyl group have been cyclized with mercury(II) acetate to give acetal derivatives of threo 1,2-diols with moderate selectivities (equation 54 and Table 15, entries 1 and 2).147 Moderate to excellent stereoselectivity has been observed in the iodocyclizations of carbonate derivatives of allyl alcohols (entries 3-5).94a The currently available results do not provide a rationale for the variation in observed stereoselectivity. 

Table 15 O-Cyclizations of Derivatives of Acyclic Allylic Alcohols (Equation 54)...

One of the amenities of present-day organic synthesis is the availability of intermediates from the many chemical supply companies. More than 100 allylic alcohols (excluding extensive listings of phorbol esters and prostaglandin structures) are offered for sale from these sources. Two concerns about such supplies should be noted. The first is the EZZ composition of acyclic allylic alcohols, which should be checked when it is not specified, and second is the optical purity of allylic alcohols offered in optically active form, which likewise should be checked. 

Hydroboration of alkenes1 (15, 91). The Rh(I)-catalyzed hydroboration provides a highly diastereoselective reaction in a synthesis of a poly ether antibiotic. Thus the derivative (1) of an acyclic allylic alcohol is converted to the primary alcohol 2 by hydroboration with catecholborane (CB) catalyzed by ClRh[P(C6H5)3]3 with 94 6 selectivity. Note that hydroboration of 1 with disiamylborane (12, 484) proceeds with the opposite selectivity at Cio (8 92). 

In recent years, most of the attention has focused on the stereocontrolled synthesis of cyclopropanes. The isolation of several structurally intriguing natural product has revived the interest of the scientific community for the development of new methods. Several efficient and practical chiral auxiliaries have been developed for the enantioselective cyclopropanation of olefins. The most efficient chiral auxiliaries have been specifically designed for the cyclopropanation of acyclic allylic alcohols (Table 13.3, entry 1, 2, Protocol 8),24 alkenones,25 cycloalkenones26 (Table 13.3, entry 3,4, Protocol 9), vinyl ethers27 (Table 13.3, entry 5, Protocol 10), and vinylboronate esters28 (Table 13.3,... 

Stereoselective cyclopropanation of acyclic allylic alcohols glucose-derived chiral auxiliary24 1... 

The enantioselective cyclopropanation of acyclic allylic alcohols can be achieved with excellent enantioselectivities when the reaction is carried out in the presence of the chiral dioxaborolane ligand 18 (Equation 13.6, Protocol 11). This reaction also features the preparation of Zn(CH2I)2 DME complex which is soluble in dichloromethane.32 This chiral additive is also very effective for the synthesis of 1,2,3-substituted cyclopropanes, when 1,1-substituted diiodoalkanes are used as precursors.33 Finally, this method has been used extensively in natural product synthesis.34... 

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