Dienes, Danishefsky

The mechanism for the hetero-Diels-Alder reaction of benzaldehyde 9 with the very reactive diene, Danishefsky s diene 10, catalyzed by aluminum complexes has been investigated from a theoretical point of view using semi-empirical calculations [27]. The focus in this investigation was to address the question if the reaction proceeds directly to the hetero-Diels-Alder adduct 11, or if 11 is formed via a Mukaiyama aldol intermediate (Scheme 8.4) (see the chapter dealing with hetero-Diels-Alder reactions of carbonyl compounds). 

IPreparation of l-methoxy-3-trimethylsilyloxybuta-l, 3-diene (Danishefsky s Idiene) and Diels-Alder addition with maleic anhydride. 

The regiochemistry of Diels-Alder reactions with 3.3.3-trifluoropropene (1) shows that the inductive effect of a trifluoromethyl group increases the magnitude of the molecular orbital coefficient of the unsubstituted terminus, but the effect is not great enough to achieve high regioselectivity with dienes other than l-methoxy-3-(trimethylsiloxy)buta-l,3-diene (Danishefsky s diene, 4) compare the reaction of 1 with 2, 3, and 4. ... 

When the trifluoromethyl group is the only electron-withdrawing. substituent of the cyclic dienophilc, such as in 4-(trifluoromethyl)-1,2-dihydronaphthalene, high pressure is required for the reaction to occur. The yield is improved when the reaction is performed with the tricarbonyl chromium complex 21 of 4-(trifluoromethyl)-l,2-dihydronaphthalene. In the reaction with l-methoxy-.3-(trimethylsiloxy)buta-l,3-diene (Danishefsky s diene, 4), the cycloadducts are obtained as a 1 1 mixture ofcHr/o/c.vo-addition products. They are easily converted into the (trifluoroniethyl)phenanthrenone 22 by the action of bromotrimethylsilane. 

Immmium salts constitute a class of generally reactive hetero dienophiles. During the past several years a number of examples have been describe of [4 + 2] cycloadditions of imines with oxygenated dienes under Lewis acid catalysis. - These reactions probably involve intermediate immonium salts which react regio- and often stereo-selectively with these electron-rich 1,3-dienes. Danishefsky and coworkers have provided several instances of this type of process. Equation (18) shows an approach to... 

This unsaturated acid was made by a Diels-Alder reaction, but not the one you might have expected. Danishefsky invented a special diene Danishefsky s diene 159 for the introduction of enone functionality in the Diels-Alder reaction and here you see an application. The Diels-Alder adduct 161 is a silyl enol ether with a leaving group in the (1-position and it hydrolyses easily to the enone 162. 

A -Aryl-2,2,2-trifluoroethanimines can act in cycloadditions as heterodienes (see Section 2.1.1.6.2.2.2.) however, with l-methoxy-3-(trimethylsiloxy)buta-l.3-diene (Danishefsky s diene 12) in the presence of a Lewis acid they can act as dienophiles, leading to one regioisomer, e.g. 13.50... 

Danishefsky reported some years ago that acyclic, unactlvated imines undergo Lewis acid catalysed cycloaddition with siloxydienes to give six-membered nitrogen heterocycles. Two reports have now extended these observations to include the reaction of cyclic imines with dienes. Danishefsky s group has also described the cycloaddition of dihydro-B-carbolines with three siloxydienes to... 

Comprehensive details of the preparation of (3 )-l-methoxy-3-trimethyl-silyloxybuta-1,3-diene (Danishefsky s diene) are now available, whilst (3 )-l,3-dimethoxybuta-1,3-diene has been prepared for the first time, with its cycloadditions being studied. ... 

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