Stereochemistry control

Browning, J Bushnell, G.W., Dixon, KR. and Pidcock, A. (1983) [PtCl(PEt3)(CH (PPhjSjj)], A Novel C,S-Bonded Chelate With Dynamic Stereochemistry Controlled By A Metal-Ligand... 

Wilhelm and Widdowson have exploited the asymmetric deprotonation of 470 in a synthesis of a protected version 478 of the biaryl component of vancomycin, actinoidinic acid (Scheme 185) " . One of the rings derives from an arenechromium tricarbonyl with stereochemistry controlled by asymmetric lithiation. The most readily lithiated position of 470, between the two methoxy groups, first needed blocking. Enantioselective... 

Asymmetric dihydroxylation (Chapter 45) is straightforward though you might like to comment on the chemoselectivity. The diol is converted into the epoxide and you should explain the regio- and chemoselectivity of this step. The next step is perhaps the most interesting what is the mechanism of the cyclization, what is the role of silicon, and how is the stereochemistry controlled ... 

The synthetic strategy of cembrane-type diterpenes include (1) efficient methods for the construction of a 14-membered carbocyclic ring, (2) functional group assembly, and (3) stereochemistry control as the key reactions. Because the... 

In the absence of any substituent at the C-6 position, the sulfur stereochemistry controls the stereochemical outcome of the [2,3]-sigmatropic reaction, and hence the imine (60) can be stereo specifically converted to the cw-thiadiazolidine (61) <88JOCl 116>. The epimeric dihydrothiazine... 

Another important version of the aldol reaction involves the use of boron enolates.A cyclic TS similar to that for lithium enolates is involved and the same relationship exists between enolate geometry and product stereochemistry. In general, the stereoselectivity is higher than for lithium enolates. The O—B bond distances are shorter than those in lithium enolates, and this leads to a more compact TS and magnifies the steric interactions that control facial stereoselectivity. As with lithium enolates, the enolate stereochemistry controls diastereoselectivity. 

A further example concerns the isolation of cyclic trimers of siloxanes." These cyclic trimers are usually short-lived kinetic products generated during the first phase of the polycondensation of trisilanols. In a bulk, they usually further condense to higher oligomers which are thermodynamically more stable and therefore, these trimers cannot be isolated. However, when the condensation of phenyltrimethoxysilane PhSi(OMe)3 is performed in the nanocage 12, only the cyclic trimer 14 is obtained under stereochemistry control giving exclusively the all-cw isomer (Scheme 10.6). 

This review of recent progress in [4+2] cycloaddition of 2-pyrone dienes emphasizes control of relative and absolute stereochemistry. Discussion includes the development of mild reaction conditions and electronic matching of reaction partners, allowing the isolation of bicyclic lactones with control of relative stereochemistry. Control of absolute stereochemistry in these cycloadditions features a stereo-chemical control element on one or more of the following a pyrone diene, a dienophile, or a Lewis acid promoter. Applications of this methodology to synthesizing complex organic molecules are mentioned. 

Copolymers from epoxides Catalyst activity, product selectivity, and stereochemistry control 12ACR1721. 

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