Acyclic stereoselection

Rh+ catalyst is more selective than Ir+ for acyclic stereoselection, Acyclic homoallylic systems ... 

It would be difficult to overestimate the role that the polyether antibiotics have played in the development of organic synthesis, particularly in the area of acyclic stereocontrol. These molecules have inspired many spectacular achievements in organic synthesis, achievements that have dramatically expanded the power and scope of the science. In fact, it would not be inaccurate to attribute much of our understanding about the factors controlling acyclic stereoselectivity for such fundamental processes as hydroboration,5 epox-... 

Over the past two decades, chiral allyl- and crotyl-boron reagents have proved to be extremely valuable in the context of acyclic stereoselection. The development of superior allyl-boron reagents, which can give enantio- and diastereoselectivities approaching 100%, has become both challenging and desirable.68... 

In contrast to the "classical solution" we have just discussed, we will now consider the aldol condensation -one of the most important carbon-carbon bond formation reactions [3], in both the laboratory and Nature l - as an example of the "contemporary solution" to the problem of acyclic stereoselection. As a reversible reaction, the design of highly stereoselective aldol and related reactions demands that all the stereochemical aspects involved in the C-C bond formation are kinetically controlled. 

ACYCLIC STEREOSELECTION. II ASYMMETRIC EPOXIDATION AND DIHYDROXYLATION OF OLEFINIC DOUBLE BONDS.277... 

MRS/acyclic stereoselection macro-cyclization by Stille coupling Nicolaou 2000A... 

For many years acyclic stereoselection has been one of the main interests in organic chemistry35. The most studied case is 1,2-induction, usually with a-chiral carbonyl compounds or olefins. 

An interesting and highly efficient method of acyclic stereoselection is as follows53. 

Only one example has been reported in which an acyclic amine was alkylated with this method32. Using the oxazoline derivative of Af-methylbenzeneamine, deprotonation, subsequent alkylation with iodomethane at — 78 °C and removal of the oxazoline moiety afforded the 7 -confi-gurated a-methylbenzenamine in high yield (95%) with a selectivity of 64% ee. This value is nearly the same as that obtained on reaction of the tetrahydroisoquinoline derivatives at that temperature. Thus, as in the case of methanimidamides, no conclusions concerning the effectiv-ity of this approach in acyclic stereoselection can be drawn at present. 

Acyclic stereoarrays are important both in themselves and as precursors to enantiomerically-defined ring systems. Although the aldol condensation has long been a workhorse for acyclic stereoselection, there are still new things being done. 

The (diastereoselective) conjugate addition of silylcuprate reagents to a variety of chiral derivatives of a,(3-unsaturated carboxylic acids can be used to prepare optically active p-silyl esters.258 259 Best results are obtained with substrates of type (25). The (related) p-silyl ketones, which also constitute valuable building blocks for (acyclic) stereoselective synthesis, are now accessible in high ee via palladium-catalyzed enantioselective 1,4-disiiylation of a,p-unsaturated ketones (Scheme 76).260... 

The rigidity of the allene and its facile formation were imaginatively exploited in a synthesis of the vitamin E side chain alcohol, in which an overall transfer of 1,4 to 1,5 acyclic stereoselection process was achieved (Scheme 8).162... 

Lodge, E. R Heathcock, C. H. Acyclic stereoselection. 40. Steric effects, as well as (T -orbital energies, are important in diastereoface differentiation in additions to chiral aldehydes, J. Ant Chem. Soc. 1987,109, 3353-3361. 

Vinyloxiranes react with nucleojAiles in three regiochemically distinct ways with a, 3 and vinyl-ogous modes of opening. The subject has been of considerable interest in the context of acyclic stereoselection and generation of allylic alcohols in an iterative fashion. 

A stereocontrolled synthesis of the vitamin E side chain alcohol was achieved in an elegant fashion (equation 121) allowing mutation from a 1,4- to a 1,5-acyclic stereoselection process applicable also to the optically active series . 

Heathcock, C. H., Hug, K. T., Flippin, L. A. Acyclic stereoselection. 27. Simple diastereoselection in the Lewis acid mediated reactions of... 

Mori, I., Ishihara, K., Heathcock, C. H. Acyclic stereoselection. 50. New stereoselective propanal/propanoic acid synthons for aldol reactions. J. Org. Chem. 1990, 55, 1114-1117. 

Whereas acyclic stereoselection in enolate alkylations is now a relatively mature field, the stereoselective alkylation of acyclic dipole-stabilized systems is virtually undeveloped. The only report to date... 

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