1 ,3-Enynes From carbonyl compounds

Scheme 2.8 Mechanism hypothesis concerning the formation of the different products from 1,6-enynes and carbonyl compounds...

S)-(-)-CITRONELLOL from geraniol. An asymmetrically catalyzed Diels-Alder reaction is used to prepare (1 R)-1,3,4-TRIMETHYL-3-C YCLOHEXENE-1 -CARBOXALDEHYDE with an (acyloxy)borane complex derived from L-(+)-tartaric acid as the catalyst. A high-yield procedure for the rearrangement of epoxides to carbonyl compounds catalyzed by METHYLALUMINUM BIS(4-BROMO-2,6-DI-tert-BUTYLPHENOXIDE) is demonstrated with a preparation of DIPHENYL-ACETALDEHYDE from stilbene oxide. A palladium/copper catalyst system is used to prepare (Z)-2-BROMO-5-(TRIMETHYLSILYL)-2-PENTEN-4-YNOIC ACID ETHYL ESTER. The coupling of vinyl and aryl halides with acetylenes is a powerful carbon-carbon bond-forming reaction, particularly valuable for the construction of such enyne systems. 

Enines derived from allylic substitution products by propargylation offer many possibilities in organic synthesis. We have pursued Au-catalyzed cycloadditions with carbonyl compounds [31], enyne metathesis reactions in combination with Diels-Alder reactions [32], and a Pauson-Khand reaction as part of a synthesis of kainic acid [33]. The latter synthesis is described in Scheme 11.16 as a ret-rosynthetic scheme. The Ir-catalyzed allylic amination under in situ conditions proceeded with excellent enantioselectivity. Overall, our synthesis required 12 steps and gave a total yield of 12%. 

In summary, a clearer picture of the intertwined reaction pathways at play in the intermolecular gold(I)-catalyzed addition of carbonyl compounds to 1,6-enynes has emerged from this study. Ultimately, this work complements the investigations leading to tricyclic compound I-IO and 1,3-dioxolanes 1-23 reported by the Helmchen group (Scheme 2.7) [Ref. 226, 228 in Chap. 1]. 

Iwasawa et al. developed a tungsten-mediated benzannulation reaction (Scheme 15.15). On treatment of o-ethynylphenyl ketones 11 with 3 equiv of preformed W(C0)5(THF), followed by the addition of electron-rich alkenes 8, such as enam-ines and enol ethers, the corresponding naphthalenes 19 were produced together with W(CO)6 [26]. Ohe, Miki, and co-workers prepared pyranyUdene-metal complexes from conjugated enyne-carbonyl compounds using Mo, W, and Cr complexes, which were treated with dimethyl acetylenedicarboxylate to give benzene derivatives [27]. 

The 14-electron species denoted here as Cp2M (M = Ti, Zr), generated from Group 4 metallocenes, mediate useful oxidative cyclizations of dienes 231 [103,104], enynes 233 [105] and diynes 235 [105,106] via the metallacycles 232, 234 and 236. These metallacycles are useful intermediates, which are hydrogenolysed, carbonylated, halogenated, attacked by electrophiles and converted to functionalized cyclic compounds such as 238 and 239 [107],... 

The formation of oxatricyclic compounds 1-2 and/or fragmentation products 1-3 was previously reported from 1,6-enynes with a carbonyl group at the alkenyl side chain such as I-l (Scheme 3.19) [Ref. 223 in Chap. 1]. 

The reaction started from the complexation of PtCla with the alkyne unit in 372 to give vinyl platinum 373. An intermediate 373 was attacked by carbonyl oxygen if the enyne compounds contained the oxygen atom at an... 

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