7-Methyl-1.3.5-cycloheptatriene

Considering both 5-methyl-1,3-cyclopentadiene and 7-methyl-1,3,5-cycloheptatriene (B), which labeled H atom is most acidic Which labeled H atom is least acidic Explain your choices. 

With toluene, in a Pyrex vessel, the products were ethylbenzene, m-and p-xylenes, and an unidentified product. In a quartz vessel o-xylene was also found and the unidentified product decreased, suggesting that the unidentified product was a methyl cycloheptatriene capable of undergoing photoisomerization to give xylenes. 

Convenient new routes to tricyclo[4,1,0,0 ]hept-3-ene and its derivatives have been disclosed. Acetone-sensitized irradiation of bicyclo[3,2,0]hept-6-en-2-one affords the ketone (624), whose enol phosphate is reduced by lithium-ammonia to give the parent alkene (625). " A second route is also described, starting from the 7,7-di-bromonorcarane derivatives (626) and (627). Reaction of (626) with methyl-lithium in ether at 0°C afforded a 3 1 mixture of the tricycloheptenes (628) and (629) similar reaction of (627) gave (630 40%), but reactions of the parent dibromide were unsuccessful. Catalytic Ag ion causes the rearrangement of (628) and (629) to, respectively, 3-methyl- and 1-methyl-cycloheptatriene. Initial Ag" attack at the least hindered edge bond is implicated. Attempted preparation of the tetrahedrane dimer (631) by the addition of dibromocarbene to homobenzvalene followed by treatment of the adduct so obtained with excess methyl-lithium in ether at 0°C afforded instead 5-ethynyl-cyclohexa-1,3-diene. 

Methyl-cycloheptatriene 34 on heating undergoes slow [l,5]-suprafacial hydrogen shift rather that [l,7]-antarafacial H-shift to yield a mixture of methyl-substituted isomers [9]. 

Scheme 95 Preparation of methylated cycloheptatrienes from methylated cyclopropenes and thiophene 1,1-dioxide [118]...

Methylated cycloheptatrienes were prepared by cycloaddition of methyl-cyclopropenes and thiophene 1,1-dioxides after expulsion of SO2 the resulting cycloheptatrienes could be used to synthesize tropylium ions (Scheme 95) [118], Benzocyclobutene reacted with thiophene 1,1-dioxides at a relatively mild temperature to give the corresponding benzocyclo-octenes 101 in acceptable yields. For example 2,5-dimethyl-, 3,4-dimethyl-, 2,3,4,5-tetramethyl-, and 2,3,4,5-tetraphenylthiophene 1,1-dioxides gave the corresponding products in 38-78% yields. Elimination of sulfur dioxide took place under the reaction conditions, but the initial adducts 100 were not observed (Scheme 96) [119],... 

The thermal rearrangements of methyl-substituted cycloheptatrienes have been proposed to proceed by sigmatropic migration of the norcaradiene valence tautomer. The first step is an electrocyclization analogous to those discussed in Section 11.1. 

These results indieate that deaminoeolehinol methyl ether is 9 12 13 14-tetramethoxy-3 4 5 6-dibenz-d = -cycloheptatriene (XI j... 

A reactivity index which accurately predicts the site selectivity of the photoisomerization of cycloheptatrienes to their bicyclic valence tautomers fails with 1//-azepines.237 For example, for methyl 2-methyl-1//-azepine-l-carboxyIatc (14), the 1-methyl isomer 16 is the predicted major product in practice the reverse is true. 

Scheme 31. Isomer distribution [%] of Rh CFjCOO -catalyzed cyclopropanation of substituted benzenes with methyl diazoacetate at 22 °C. The numbers refer to the percentage of 1,3,5-cyelohepta-triene-7-carboxylate from the total cycloheptatriene isomers.

EA 5302 l-Methyl-4-piperidyl Isopropylphenylglycolate (33%) and l-Methoxy-l,3,5-cycloheptatriene (CH) Mixture C12-A006... 

Starting from 2,4,6-octatriene and pivaldehyde, the conjugated homoallylic alcohol 8 is obtained as the sole product. Cycloheptatriene-derived complexes react with aldehydes and C02 to afford mixtures of the isomeric 1,3- and 1,4-cycloheptadienyl carbinols or acids, respectively. Interestingly, analogous reactions with methyl chloroformate or dimethyl carbamoyl chloride produce the conjugated dienyl ester 9 or amide 10 as unique products [19,20]. 

Scheme 6.108 Products ofthe interception of 1,2,4,6-cyclohepta-tetraene (5) with 1,3-diphenylisobenzofuran, anthracenes, 2,5-dimethyl-3,4-diphenylcyclopenta-2,4-dien-l-one, methyl 2-pyrone-5-carboxylate, tropones, 8,8-dicyanoheptafulvene and 1,3,5-cycloheptatrienes.

Dehydration products have been observed from photosensitized oxygenation reactions with cycloheptatriene (304),220 AMialin (307) 222 3/1- and 3a-hydroxy-A4-cholestenes (312a and 312b, respectively),226,227 and 2-hydroxy-10-methyl-1,9-octalin (316).226... 

The bicyclic 3,4-dihydropyridines (51) and (53) illustrate that the electrocyclic ring opening is sensitive to substituents (80TL599). The 3,4-dihydropyridine (51) has been observed to be in equilibrium with the azepine (50). Consistent with the analogous carbocyclic system, norcaradiene-cycloheptatriene, the monocycle (50) is the predominant species present in this equilibrium. In contrast, the dimethyl derivatives (52) and (53) exist almost exclusively in the 3,4-dihydropyridine form. A greater steric interaction between these methyl substituents in (52) was given in explanation of these observations. 

Recently, a new reactivity index has been proposed (80H(14)1717> which predicts accurately the site selectivity of photocyclization of substituted cycloheptatrienes to their bicyclic valence tautomers. Unfortunately, application of the method to substituted lH-azepines is far less successful. For example, for 2-methyl-l-methoxycarbonyl-lH-azepine (37 R = 2-Me) AGrs values for C-2—C-5 and C-4—C-7 cyclization are calculated as 0.093 and 0.040 kJ mol-1, respectively, i.e. predicting the 1-methyl isomer (39) as the major product. Experimentally, however, the reverse is true, the yields being 93.5% for 3-methyl (38 R = Me) and 6.5% for 1-methyl (39 R = Me). The corresponding photoinduced valence isomerizations of 1-benzazepines to 3,4-benz-2-azabicyclo[3.2.0]hepta-3,6-dienes (38a) have been recorded (80JOC462). These isomerizations have also been achieved thermally in the presence of silver ion (80TL3403). 

Thermal 1,5 hydrogen shift of cyclopentadiene and 1,3,5-cycloheptatriene, and methyl shifts in the corresponding methyl-substituted derivatives and in methyl-1,3-... 

---