Bicycle product

Generally, for E-dienes, the fused product is observed unless the connecting chain is very long. For Z-dienes, either the fused or bicyclic products are possible. 

Recently, various monosaccharides have been employed as a source of 1,4-dicarbonyl compounds for pyridazine syntheses 70CB1846, 74CPB1732, 75JHC957). Moreover, diacylcyc-lopropanes have been also reported to give pyridazines the bicyclic products are transformed by P4S10 into the corresponding 3-thioxopyridazines 80JHC541). 

The bicyclic product is formed by coupling of the two radical sites, while the alkene results from an intramolecular hydrogen-atom transfer. These reactions can be sensitized by aromatic ketones and quenched by typical triplet quenchers and are therefore believed to proceed via triplet excited states. 

These various photoproducts are all valence isomers of the normal benzenoid structure. These alternative bonding patterns are reached from the excited state, but it is difficult to specify a precise mechanism. The presence of the t-butyl groups introduces a steric factor that works in favor of the photochemical valence isomerism. Whereas the t-butyl groups are coplanar with the ring in the aromatic system, the geometry of the bicyclic products results in reduced steric interactions between adjacent t-butyl groups. 

Allylsulfonyl chloride and enamines furnished the sulfonyl enamines or cyclic sulfones 704), and alkyldisulfonyl chlorides gave 1 2 adducts or bicyclic products with morpholinocyclohexene. 

Bond-Huper [69JCS(C)2453] synthesis, no traces of the described high-melting dark red substance were found. Only tolane-2-carboxylic acid amide (yield 65%) was obtained—the white crystals with a melting temperature of 156-157°C— which coincided with the results of Castro et al. (66JOC4071). Thus, in conditions of acetylide synthesis, o-iodobenzamide forms no bicyclic product. 

The R depends on the amine R NH2 used in the reaction. When ammonia was used a bicyclic product (7) was formed from nitro-ethane. ... 

Propargylsilanes can also be employed in the Sakurai reaction. For example the enone 6, containing a propargylsilane side chain, undergoes an intramolecular Sakurai reaction, catalyzed by an acidic ion-exchange resin—e.g. Amberlyst-15—to give stereoselectively the bicyclic product 7 in good yield ... 

Heating (1Z,3Z,5Z)- 1,3,5-cyclooonatriene to 100 °C causes cvclization and formation of a bicyclic product. Is the reaction conrotatory or disrotatory What is the stereochemical relationship of the two hydrogens at the ring junctions, cis or trans ... 

Intramolecular allylzinc aldehyde additions lead, in one synthetic step, to bicyelic a-methylene-y-lactones41. Interestingly, the (Z)-isomer gave only the r/5-fused bicyclic products, which arises from a. vyw-selectivc addition, while the ( >isomeric bromide furnished a cisjtrans mixture (yield 56%, cisjtrans 72 28)41 indicating that the double-bond torsion and the intramolecular carbonyl addition have similar rates. A similar sequence was the key step in a confertin synthesis28. 

The first cyclization gives a mixture of cis- and from -isomers and only the cis-isomer goes on to give bicyclic products. The relatively slow rate of the second cyclization step, and the formation of rrou.s-product which does not cyclize, provides an explanation for the observation that radical polymerizations of triallyl monomers often give a crosslinked product. 

Due to the two electron-donating groups in the bicyclic product 150 and the unhydrolyzed precursor of 148, they should be quite reactive dienes in Diels-Alder reactions. However, such [4+2] cycloadditions were observed only for the cyclohexane-annelated cyclopentadienes 151b, which equilibrate with the more reactive isomers 154 by 1,5-hydrogen shifts (Scheme 33). The [4+2] cycload-... 

Intramolecular versions of the Diels-Alder reaction are well known, and this is a powerful method for the synthesis of mono- and polycyclic compounds.There are many examples and variations. One interesting internal Diels-Alder reaction links the diene and dienophile by a C—O—SiR2—or a C—O—SiR2—O—C linkage. Internal cyclization to give a bicyclic product is followed by cleavage of the O-Si unit to give a monocyclic alcohol. 

A deviant reaction was observed when the AT-Boc-aziridinecarboxamide 44b was treated with LDA in THF as the base. Under these kinetically controlled conditions an intramolecular reaction of the amide nitrogen with the Boc group takes place leading to the bicyclic product 46 in which the aziridine ring is retained (Scheme 36) [45]. 

Fig. 10. Formation of bicyclic products in the aminolysis reaction of the tetrameric compounds.

The intramolecular reductive aldol reaction of keto-enones was successfully conducted under conditions similar to those described above, employing a cationic Rh complex and PI13P (Scheme 20) [34]. The keto-enone 63 was cyclized in the presence of added K2CO3 to give the ketone-aldol 64 in 72% yield with exclusive ds-selectivity. Dione-enone derivatives, for example 68 and 70, were efficiently cyclized to furnish bicyclic aldol products 69 and 71, respectively, wherein three stereogenic centers of the bicyclic product form stereoselectivity through the intermediacy of a Rh-enolate. 

An enantioselective variant of the diene cydization reaction has been developed by application of chiral zirconocene derivatives, such as Brintzinger s catalyst (12) [10]. Mori and co-workers demonstrated that substituted dial-lylbenzylamine 25 could be cyclized to pyrrolidines 26 and 27 in a 2 1 ratio using chiral complex 12 in up to 79% yield with up to 95% ee (Eq. 4) [ 17,18]. This reaction was similarly applied to 2-substituted 1,6-dienes, which provided the analogous cyclopentane derivatives in up to 99% ee with similar diastereoselectivities [19]. When cyclic, internal olefins were used, spirocyclic compounds were isolated. The enantioselection in these reactions is thought to derive from either the ate or the transmetallation step. The stereoselectivity of this reaction has been extended to the selective reaction of enantiotopic olefin compounds to form bicyclic products such as 28, in 24% yield and 59% ee after deprotection (Eq. 5) [20]. 

Pyridotriazinone 70 was obtained by the reaction of iV-(2-pyridyl)benzoylacetamide 119 with nitrosobenzene in methanol. The reaction probably involves the attack of two molecules of nitrosobenzene at C-2 of 119 with cleavage of C(l)-C(2) and C(2)-C(3) bonds affording diphenylcarbodiimide and 2-pyridylisocyanate, which undergo a [4+2] heterocycloaddition. Interestingly, the reaction of acetyl analog of 119 did not afford the corresponding bicyclic product, instead, 2-methoxy-2-phenylamino-iV-(2-pyridyl)acetoacetamide was obtained (Equation 14) <2004S2975>. 

The Diels-Alder reaction of isopyrazoles 365 with MTAD gives azoalkanes 366. Direct as well as triplet-sensitized (benzophenone) photolysis of these compounds leads to the corresponding housanes (bicyclo[2.1.0]pentanes) 367. Under acidic conditions, the housanes rearrange to the corresponding bicyclic products 368 <1995JOC308,... 

Treatment of 467 with more than 2 molar equiv of the corresponding aldehyde gives bicyclic products 468 in good yields. These compounds are useful intermediates in the tandem cycloreversion-cycloaddition process (Equation 58) <2000S1170, 2002S 1885>. 

For 4-nitrophenyl 2-azadiene 617, vigorous reaction conditions are necessary (110°C, sealed tube, 25h) and give bicyclic product 619. The formation of this compound could be explained by [4+2] cycloaddition reaction leading to 618 followed by dehydrogenation (Scheme 99) <1994T12375, 2003H(61)493>. 

Furans and some of its derivatives have been cyclopropanated with the ketocarbenoids derived from ethyl diazoacetate and copper catalysts. The 2-oxabicyclo[3.1.0]hex-3-enes thus formed are easily ring-opened to 1,4-diacylbutadienes thermally, thermo-catalytically or by proton catalysis 14,136). The method has been put to good use by Rh2(OAc)4-catalyzed cyclopropanation of furan with diazoketones 275 to bicyclic products 276. Even at room temperature, they undergo electrocyclic ring-opening and cis, trans-dienes 277a are obtained with fair selectivity 257,258). These compounds served as starting materials in the total syntheses 257 259) of some HETE s (mono-... 

Tris(a-hydroxy-/3,/3,/3-trichloroethyl)phosphine reacts with phenyl-trichlorosilane, phosphorus, and arsenic trichlorides in the same way, giving bicyclic product (14) [Eq. (12)] (78ZOB2437). 

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