2.5- Heptadiene synthesis

Borabicyclo[6.1.0]hepta-2,4-diene, heptaphenyl-structure, 1, 661 7-Borabicyclo[2.2. l]heptadienes synthesis, 1, 660... 

Reinhoudt et al.53) have reported the first synthesis of a monocyclic thiepin stabilized by electronic effects of the substituents. This synthesis utilizes the idea described in Section 2.3.3. 3-Methyl-4-pyrrolidinothiophene (85a) was treated in deuteriochloroform at —30 °C with dimethyl acetylenedicarboxylate. H-NMR monitoring of the reaction indicated that a [2 + 2]cycloaddition proceeded slowly at this temperature giving the 2-thiabicyclo[3.2.0]heptadiene (86a) which rearranged via ring opening of the cyclobutene moiety to the 4-pyrrolydinylthiepin (87a). At the... 

The unsubstituted quinazolidine system 5 was constructed from mesylate 173. The key feature in this synthesis is based on a cyclohydrocarbonylation of the protected 4-amino-l,6-heptadiene 169 catalyzed by Rh(acac)(CO)2-BIPHEPHOS. Formation of the hemiamidal-aldehyde 171 took place by hydroformylation of the two olefin moieties and cyclization. Elimination of water gave 172, which, after treatment with NaBFE, subsequent mesylation to 173, and catalytic hydrogenation, afforded 5 (Scheme 29) <1998TL4599>. 

Reaction of iodine with non-conjugated dienes has been applied to the synthesis of cyclic compounds100. Although the reactions of 1,5-hexadiene, 1,6-heptadiene and 1,7-octadiene with I2 in CCI4 gave exclusively products arising from addition to the two double bonds, the introduction of dialkyl substituents into the 4-position of 1,6-heptadiene completely changed the reaction course in favor of cyclization (equation 85). 

The thermal lability of 7-azabicyclo[2.2.1]heptadiene derivatives is the main factor limiting their availability by synthesis (see Section II,... 

Interestingly, zirconacyclopentane 246 formed by the reaction of 1,6-heptadiene with the Zr complex has the firms ring junction mainly [108]. It should be noted that the preparation of the trans ring junction in the bicyclo[3.3.0]octane system by other means is difficult. Carbonylation of 246 affords trans-fuzed bicyclo[3.3.0]octanone 247 [109,111]. The diacetoxy compound 248 is obtained by oxidative cleavage of 246. Protonation affords the frans-dimethylcyclopentane skeleton. Similar reactions occur with 1,6-enynes, and Pauson Khand-type cyclopentenone synthesis is possible by carbonylation. 

Pyrrole has also been utilized to some extent as a diene in Diels-Alder reactions to give functionalized 7-azabicylo[2.2.1]heptenes and 7-azabi-cyclo[2.2.1]heptadienes.4 While the synthetic utility of this reaction is limited by the aromatic stability of the pyrrole ring, the use of Lewis acids, electron-withdrawing groups on the pyrrole, alkyne dienophiles, and high pressures have allowed pyrroles to be employed in the synthesis of several azanorbomane targets.4... 

Synthetic applications of the reaction are somewhat limited as the highly reactive biradicals and radical pairs tend to undergo reactions that compete with C—C bond formation. As in previous cases, the reaction may have synthetic value for the synthesis of strained structures involving small rings. For example, the preparation of the simplest [2]-ladderane 55 by photodecarbonylation of bicyclo[3.2.0]heptan-3-one 54 gave the bicyclic structure in 5% yield with a ring-opened 1,5-heptadiene being the dominant product (Scheme 2.14) [41]. 

Me3SiCN is a convenient, reactive cyanide donor in transition metal-catalyzed processes. The Pd-catalyzed reaction of aryl iodides with Me3SiCN is useful for the synthesis of aryl cyanides.257 Me3SiCN works also as an effective co-catalyst for the Pd-catalyzed cyanation of aryl iodides with KCN.258 Allylic acetates, carbonates, and the related compounds undergo the Pd-catalyzed cyanation with Me3SiCN.259-261 The tandem cyclization-cyanation reaction of 2-bromo-l,6-heptadienes with Me3SiCN proceeds under catalysis by an Ni complex (Equation (68)).262... 

The method of choice for the synthesis of borepins, benzoborepins, and heterole-fused borepins is reaction of the corresponding stannepins with boron trihalides or aryl dihaloboron compounds (see Section 14.20.10). A dibenzodi-hydroborepin has been prepared by a [6+l]-type cyclization of a naphthalene-1,8-diborane with BC13 (see Section 14.20.9.1). Yields of these methods are comparable. The saturated systems are typically prepared by reaction of 1,6-heptadienes with monoalkyl boranes such as thexyl borane (see Section 14.20.6.1). 

The chiral Diels-Alder adduct 19 is a versatile intermediate for the synthesis of many chiral bicyclo[2.2.1]heptadienes, because the tri-n-butylstannyl group can be replaced by halogen or a wide variety of carbon appendages, the latter by use of either copper-mediated or palladium-catalyzed cross-coupling reactions. For example, as shown in Eq. (34), reaction of 19 with A-iodosuccinimide produced the iodo aldehyde 12 in 92 % yield. Coupling of 12 with ( )-/ -styryl-tri-n-butylstannane and either 1.5 equiv. copper(I) 2-thiophenecarboxylate (CuTC) or catalytic PdCl2(CH3CN)2 afforded the triene aldehyde 20 [34]. 

Nucleophilic 1,4- and 1.6-additions of cuprates and other organometallic reagents to acceptor-substituted dienes have been utilized extensively in target-oriented stereoselective synthesis - . Schollkopf and coworkers reported the diastereoselective 1,6-addition of a bislactim ether-derived cuprate to 3,5-heptadien-2-one (90% ds equation 17). The corresponding reactions of dienoates were conducted with the lithiated bislactim ether and proceeded with diastereoselectivities of >99% ds (equation 18) the adducts could be converted easily into diastereo- and enantiomerically pure amino acid derivatives. 

---