Additions vinylogous

Additive and Vinylogous Additive Pummerer Reactions Sila-Pummerer Reactions Preparation ofTrimethylsiloxy Sulfides The Abnormal Pummerer Reaction... 

Vinyl sulfoxides also partake in additive Pummerer reactions. Of particular interest in this category are cases where the sulfoxide activating agent also provides the internal nucleophile. Two general pathways for such vinylogous additive Pummerer reactions are presented in Scheme 36. ... 

These vinylogous additions are the reverse of the vinylogous eliminations and are sometimes called 1,4-additions. The electrophile adds to form the allylic carbocation that can add the nucleophile at either end. The overall process, a vinylogous Ad 2, often produces a mixture of 1,2 and 1,4 addition products (see Section 8.3.6 for details). 

Dispiro[5.0.5.1]trideca-l,5,8,12-tetraone (10) underwent ring opening with formic and acetic acid at room temperature with formation of the vinylogous addition products 11. ... 

Also alkynes have been used for the synthesis of dithiolanes. Thus, 2,3-dithioquinoxaline (355) gave, by vinylogous addition onto 3-oxo-l-alkynes (356) 2-(2-oxoalkyl)-l,3-dithiolo[4,5-i]qui-noxalines (357) (Equation (73)) <82KGS1489>. 

An ammonia molecule that is obtained by the hydrolysis of glutamine is then added to the position 4 carbon and the bond between the substrate and lysine 274 is broken by way of a second vinylogous addition/ elimination reaction. The overall reaction sequence is similar to the biosynthetic formation of anthranylic acid that serves as a biosynthetic precursor of tryptophan. 

Until now, conversions in the alkyl ehain of unsaturated fatty aeids have been developed preferentially at the double bond in eleetrophilic (1 ) or radical additions (5), in cycloadditions (6,7), and in metathesis (8). If the double bond is conjugated to a carbonyl group, the vinylogous addition of nueleophiles to the double bond becomes possible (Miehael-addition) this leads to a rich synthetic chemistry (9,10). 

Qin T, Johnson RP, Porco, JA Jr (2011) Vinylogous Addition of Siloxyfurans to Benzopyryliums A Concise Approach to the Tetrahydroxanthone Natural Products. J Am Chem Soc 133 1714... 

Scheme 20.22 The additive Pummerer reaction, competition with vinylogous addition.

While Lewis acids normally enable l,2-additi(Mis of silyloxy furans to a,(3-unsaturated aldehydes, the MacMillan group discovered that iminium catalysis favors 1,4-additions, thus overcoming the deficiency of normal Lewis acids in Mukaiyama-Michael additions 244). The high potential of this protocol was demonstrated impressively in a short synthesis of the Penicillium spiculisporum fermentation product spiculisporic acid (262). As shown in Scheme 60, vinylogous addition of the silyloxy furan 263 to the acceptor 264 catalyzed by 228 furnished the key intermediate 265 in good enantio- and diastereoselectivity. It is worth noting that the TfOH salt of the catalyst in combination with methyl ester 266 as a Michael acceptor gave the anh-diastereomer 267 exclusively. This compound was then used for the synthesis of 5-epi-spiculisporic acid (268) (Scheme 60) 244). 

In 2007, the Jorgensen group reported a highly enantioselective procedure for the conjugate addition of oximes to a,p-unsaturated aldehydes in the presence of a chiral amine catalyst (296). This protocol was later expanded to the one-pot synthesis of optically active p-diols by carrying out a vinylogous addition of oxime 317 to different a,p-unsaturated aldehydes in the presence of catalyst 276 followed by a direct reduction of the primary addition product with LiAlHj (297). 

A direct vinylogous addition of deconjugated butenolide to enals can be catalysed by aminal-pyrrolidine (153) at 15mol% loading in toluene at room temperature with... 

The bulky dirhodium tetrakis (triphenylcyclopropanecarboxylate) complex 59 catalyzes the enantioselective vinylogous addition of nitrones to terminally substituted vinyl diazoacetates to afford vinyl rhodium intermediates 60 that undergo a [3 + 2] annulation to 2,5-dihydroisoxazoles 61 (13JA14516). 

Isopropenyl acetate acts as an acetyl transfer reagent in vinylogous additive Pummerer reactions, providing an efficient means for the conversion of vinyl sulfoxides to a-acyl sulfides (167 equation 29). 

Scheme 2.38 Consecutive conjugate addition of vinylcopper reagent 126 and vinylogous addition of enolate 128 in stereoselective prostaglandin synthesis R = SifBuMej.

The carbanion -type reactivity of dienamine activation can be promoted by a silyl-protected diarylprolinol catalyst in the presence of reactive electrophilic species, such as nitroolefins or diarylmethanols (Scheme 2.10) [20]. Although both direct addition (a-addition) and vinylogous addition (y-addition) are viable reaction pathways, the a-reactivity is the more typical one and usually provides better selectivities due to more effective shielding of the a-position by the aminocatalyst. Interestingly, the a-/y-selectivity of dienamine-mediated carbanion -type addition reactions seems to be strongly influenced by the substitution pattern of the enal reactant For example, it was demonstrated that y,y-disubstituted enals favor the a-addition product while y-functionaUzation is the predominant reaction pathway for y-monosubstituted enals. 

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