Dienes reactions with aldehydes

Danshefsky s diene [19] is the 1,3-butadiene with amethoxy group at the 1-position and a trimethylsiloxy group at the 3-position (Scheme 18). This diene and Lewis acids extended the scope of hetereo-Diels-Alder reactions with aldehydes [20], This diene reacts with virtually any aldehyde in the presence of Lewis acids whereas dienes usually react with only selected aldehydes bearing strongly electron accepting a-substituents. There are two (Diels-Alder and Mukaiyama aldol) reaction pathways (Scheme 18) identified for the Lewis acids catalyzed reactions of Danishefsky diene with aldehydes [21, 22]. The two pathways suggest that these reactions occur on the boundary between the delocahzation band (the pericyclic... 

A phenyl substituent at the y-carbon atom is a much weaker electron donor in comparison with the discussed above ethoxy and morpholin-4-yl groups. Nevertheless, l-(y-phenylallyl)benzotriazole 484 is still lithiated exclusively at the carbon a as it is evident from its reaction with aldehydes and ketones leading to dienes 486, resulting from... 

Schaus et al.41 have also reported an asymmetric hetero Diels-Alder reaction of Danishefsky s diene 10042 with aldehyde 101 catalyzed by chromium(III) complex 99 bearing a similar chiral salen ligand. Product 102 is obtained in moderate to good yield and stereoselectivity (Scheme 5-31 and Table 5-5). 

The mode of reaction of titanacydobutenes with carbonyl compounds is largely dependent on steric factors (Scheme 14.31) [72]. Ketones and aldehydes tend to insert into the titanium—alkyl bond of 2,3-diphenyltitanacydobutene, and homoallylic alcohols 70 are obtained by hydrolysis of the adducts 71 [65a,73]. On the contrary, when dialkyl-substi-tuted titanacydobutenes are employed, the reaction with aldehydes preferentially proceeds through insertion into the titanium—vinyl bond. Thermal decomposition of the adducts 72 affords conjugated dienes 73 with E-stereoselectivity as a result of a concerted retro [4+2] cycloaddition [72]. 

It has been shown22 that the reaction of the diene 4 with aldehydes RCHO in the presence of a catalyst prepared from (R)-BHMOL (33) and Ti(OPr-i)3, which affords the dihydro-y-pyrones 35 in good yields and high ee, proceeds by a two-step sequence via the open-chain adducts 34, which cyclize to the products on treatment with trifluoroacetic acid (equation 20). 

The //////-substituted benzocyclobutenes 601 undergo bond reorganization under mild conditions to form ortho-quinone dimethide intermediates 602, which function as dienes in an hDA reaction with aldehydes to afford all syn-substituted isochromans 603 in excellent yield (Scheme 129) <2000AGE1937>. 

The 2,4-dialkoxy-l.l-difluoro-l,3-diene 11 undergoes [4-f 2]-cycloaddition reactions with aldehydes in the presence of Lewis acids. Dienes with a greater number of fluorine atoms tend to be less reactive and [2 -F 2]-cycloaddition reactions can predominate for example, 1,1,4,4-tetrafluorobuta-1,3-diene preferentially undergoes [2 -F 2]-cycloaddition reactions (see Section... 

The synthetic applications of McjSi /NBuj are illustrated by the reaction with aldehydes and 1,3-dienes (Scheme 35) (S9). 

N-acylaziridines occurs on treatment with triphenylphosphine with the formation of the ylides (67), thereby providing a route to a-substituted primary allylic amines via their in situ reactions with aldehydes.The reactions of triphenylphosphine with epoxides in phenolic media provide a new access to the vinyl-phosphonium salts (68). A route to 1-hydroxyalkylphosphonium salts is provided by the reactions of trimethyl- or triethyl-phosphine with aldehydes or ketones in the presence of anhydrous acids. The related 1-trimethylsiloxyalkylphosphonium salts can be isolated in the presence of trimethylsilyl chloride.Further Wittig-products have been isolated from the reaction of 1,2,3-indanetrione with triphenylphosphine, and, in related work, it has been shown that furoin is deoxygenated on heating with triphenylphosphine to form 2-furfuryl(2-furyl)ketone and triphenylphosphine oxide.The structure of the blue product from the reaction of triphenylphosphine with 2,3,5,6-tetracyano-7-oxabicyclo(2,2,1]hepta-2,5-diene has now been shown by X-ray techniques to be the stable ylide (69). ... 

Allylic arsonium ylides show a similar pattern of reactivity. Ethoxycarbonylallyl ylides, wherein the ester group is conjugated with the ylidic carbon atom, gave dienes in reactions with aldehydes or ketones , whereas other allylic ylides lacking such an electron-withdrawing substituent gave vinylic epoxides in high yield e.g. equation 8. In the... 

Grieco et al. have demonstrated that an ethereal solution of LiClO4 is useful for the diastereoselective HDA reaction of Danishefsky s diene 102 with a-amino aldehydes by chelation and non-chelation control (Scheme 10.110) [296]. According to a report by Reetz et al., a catalytic amount of LiClO4 suspended in f J I. Gf, efficiently promotes similar reactions with aldehydes and imines [297]. 

New work on the asymmetric hetero DA reaction as a route to 2,3-dihydropyran-4-ones includes the use of axially chiral biaryl-based diols <05JA1336> and chiral Bronsted acids <05TL6355> which work through hydrogen bonding. Polymer-bound Danishefsky s diene derived from acetoacetate has been used in the hetero DA reaction with aldehydes. With a chiral BINOL-Ti(IV) complex, good yields of 2-aryl-5-methoxycarbonyl-5,6-dihydropyran-... 

Initial investigations of chiral aldehydes by Danishefsky - demonstrated that both ZnCh and BF3-OEt2 exhibited high Cram, Felkin-Ahn (CF) - stereoselectivity. The cyclocondensation reaction of diene (14) with aldehyde (18) (2-phenylpropanal) under BF3-OEt2 catalysis was found to give a 4.3 1 mixture of the trans-CF dihydropyrone (19) and the cis-CF dihydropyrone (20). Only traces of anti Cram-Felkin (ACF) products are isolated. Under ZnCh catalysis, however, an 8 1 mixture of the cis-CF product (20) and the ci s-ACF product (21) is obtained (Scheme 4). A detailed analysis of these stereochemical issues is given later in Section 2.5.3.1. 

Midland has used the cyclocondensation reaction with activated dienes to synthesize pstelotin A (165 Scheme 45). The key step in the Midland synthesis is the ACF addition of diene (162) with aldehyde (161) to give (164), using Eu(hfc)3 as catalyst. Deprotection of the benzyl group gave the target molecule (165). 

A total synthesis of the monensin lactone is summarized in Scheme 50. The crucial point of this synthesis is the hetero Diels-Alder reaction of triethylsilyloxy diene (179) with aldehyde (180), carried out with 10 mol % of Yb(fod).i to give the syn Diels-Alder cycloadduct (181) as the only isomer. Compound (181) is treated with HF in pyridine and MeOH to obtain ketone (182), which is converted into the monensin lactone (183). 

In the synthesis of zincophorin, two cyclocondensation reactions are also used. In the first cyclocondensation reaction, trimethylsilyloxy diene (14) reacts with aldehyde (193) using anhydrous MgBr2 as the catalyst to give the anti-ACF pyrone (194) in 80% yield (Scheme 53). The syn.anti ratio in this reaction is 7 1. After a series of standard manipulations aldehyde (19< ) is obtained. In the second cyclocondensation reaction, anti-CF pyrone (197) results from reaction of the (4 )-r-butyidimethylsilyloxy diene (195) with aldehyde (19< ) under BF3-OEt2 catalysis (197) and its syn-CF isomers are obtained in a ratio of 4 1 and overall yield of 68%. The anti-CF aldol product is purified and cyclized to anti-CF pyrone (197) in benzene using pyridinium p-toluenesulfonate as a catalyst. Pyrone (197) converted into zincophorin (198) by a sequence of steps shown in Scheme 52. 

Homoallylic metallic species are generated from dienes in the presence of ent-SlYi and diastereoselective reaction with aldehydes has been observed. ... 

Alkylation. Lithiation and reaction with aldehydes provide a-vinyl-/3-hydroxy-phosphonates, which are precursors of 2-diethylphosphonyl-1,3-dienes. The dehydration is easily accomplished with DCC-CuCh in refluxing CH2CI2. 

Allylzirconocene chlorides. These reagents are formed from allenes. A route to l-alken-4-ols by reaction with aldehydes has been developed. 1,1-Bimetallic species derived from allenylstannanes condense with aldehydes to form 1,3-dienes. ... 

A new route to 1,3-dienes is provided by tandem nucleophilic addition to the dienylphosphonium salt (44) followed by reaction with aldehydes.2 6 An attempt to extend the reaction to provide a triene via the vinylogue of... 

Stork s strategy towards racemic morphine comprises a Diels-Alder cycloaddition reaction of a benzofuran to establish the B- and C-ring of morphine as the key step [53]. The reaction sequence started with the ketahzation of iodoisovaniUin 97 (Scheme 15). Subsequently, the phenol was reacted with methyl propiolate to afford 98 as precursor for the installation of the benzofuran moiety via a palladium-catalyzed Heck cyclization (99). Next, the key intermediate was prepared for the Diels-Alder reaction. Hydrolysis of the acetal under acidic conditions and Wittig homologation afforded aldehyde 100, which was converted to diene 101 via hydrozirconation of acetylene 105 employing the Schwartz reagent and subsequent reaction with aldehyde 100 followed by sUylation of the secondary alcohol. 

Table 1. The reaction of diene 102 with aldehydes 73c, 73d, 106a, and 106b...

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