Umlagerungsreaktionen von (2′-Propinyl)cyclohexadienolen und -semibenzolen

Rearrangements of (2′-Propinyl)cyclohexadienols and -semibenzenes The acid-catalyzed dienol-benzene rearrangement of 3- and 5-methyl-substituted (2′-propinyl)cyclohexadienols has been investigated. Treatment of the dienols with CF₃COOH in CCl₄ yields allenyl- and (2′-propinyl)benzenes via [3,4]- and [1,2]-sigmatropic rearrangements, respectively. The reaction with H₂SO₄ in Et₂O leeds to a mixture of allenyl-, 2′-propinyl-, 3′-butinyl- and (2′,3′-butadienyl)benzenes (Scheme 3). The latter are products of a thermal semibenzene-benzene rearrangement (cf. Scheme 9). The corresponding semibenzenes have been prepared by dehydration of the cyclohexadienols with H₂SO₄ or POCl₃ (Schemes 6 and 7). Under acidic conditions, the p-(2′-propinyl)semibenzenes 33–35 (Scheme 8) undergo [3,4]- and [1,2]-sigmatropic rearrangements to give again allenyl- and (2′-propinyl)benzenes, whereas the thermal rearrangements to the 3′-butinyl- and (2′,3′-butadienyl)benzenes (Scheme 9) involves a radical mechanism. In contrast, the o-(2′-propinyl)semibenzene b (Scheme 7) leads to (2′,3′-butadienyl)benzene 32 via a thermal [3,3]-sigmatropic rearrangement.     

Thermische und photochemisch induzierte intramolekulare, 1,3-dipolare Cycloadditionen von 4-Phenyl-3-(2-allylphenyl)-sydnon. Vorläufige Mitteilung. 53. Mitteilung über Photoreaktionen

Thermal and photochemically induced intramolecular 1,3-dipolar cycloaddition reactions of 4-phenyl-3-(2-allylphenyl)-sydnone The title compound 9 was synthesised in the usual way, starting from 2-allylaniline and ethyl 2-bromo-2-phenylacetate, via the nitrosaminacid 8 (Scheme 2). 9 reacts at room temperature with its potential azomethinimine-function in an intramolecular [3+2]-cycloaddition to give the tricyclic compound 11 (Scheme 2). On irradiation, 9 yields the dihydro-3H-pyrazolo[2,3-a]indole 10 which probably arises by intramolecular [3+2]-cycloaddition of the corresponding intermediate nitrilimine.     

Repetierbare Ringerweiterungen durch [2,3]-sigmatropische Umlagerungen in cyclischen Allylsulfonium-allyliden; Synthese von mittleren und grossen Thiacyclen. Vorläufige Mitteilung

Repeatable ring expansions by [2,3]-sigmatropic shifts in cyclic allylsulfonium allylides; synthesis of medium- and large-sized thiacycles Allylation of a 2-vinyl thiacyclus with allyl bromide in 2,2,2-trifluoroethanol followed by ylide generation by use of aqueous potassium hydroxide results in a [2,3]-sigmatropic rearrangement with formation of a new 2-vinyl thiacyclus enlarged by three carbon atoms (Scheme 1). In this way, starting from the 5-membered ring 1 , a series of four ring enlargement sequences leads to the 17-membered thiacycles 9 and 10 via the 8-, 11- and 14-membered rings 4 , 7 and 8 (Scheme 2).     

Synthese und thermisches Verhalten von 6,8-Dimethylentricyclo[3.2.1.02,7]oct-3-enen; [3s 3s]-sigmatropische Umlagerungen von 6-Allenyl- und 6-Propargly-1- Methylen-cyclohexa-2,4-dienen in aromatische Kohlenwasserstoffe als Beispiele für konzertierte Semibenzol → Benzol-Umlagerungen

The tricyclic dimethylene hydrocarbons 5 , 6 , 7 , 8 and d₂- 5 , (Scheme 2), which are prepared by Wittig-reaction from the corresponding ketones, are rearranged, by heating, to 4-aryl-but-1-yne derivatives via the unstable 6-allenyl-1-methylene-cyclohexa-2, 4-diene intermediates (e.g. Scheme 14). Using the deuterium-labelled compound d₂- 5 , it was shown that the allenyl moiety, formed by a retro-Diels-Alder reaction (cycloreversion) of the tricyclic dimethylene compound, migrates with complete inversion in the final o-semibenzene-benzene rearrangement (Schemes 11 and 14). Reaction of 6-propargyl-cyclohexa-2, 4-dien-1-ones with triphenylphosphonium methylide gives 6-propargyl-1-methylene-cyclohexa-2 4-dienes, which immediately undergo a [3s, 3s]-rearrangement to form 4-aryl-buta-1, 2-dienes (Scheme 9). In contrast, the rearrangement of the corresponding 4-propargyl-1-methylene-cyclohexa-2, 5- dienes proceeds by a radical mechanism (Schemes 10 and 13).     

Photocycloaddition of Cyclohex‐2‐enones to 2‐Methylbut‐1‐en‐3‐yne

Irradiation (350 nm) of 2‐alkynylcyclohex‐2‐enones 1 in benzene in the presence of an excess of 2‐methylbut‐1‐en‐3‐yne ( 2 ) affords in each case a mixture of a cis‐fused 3,4,4a,5,6,8a‐hexahydronaphthalen‐1(2H)‐one 3 and a bicyclo[4.2.0]octan‐2‐one 4 (Scheme 2), the former being formed as main product via 1,6‐cyclization of the common biradical intermediate. The (parent) cyclohex‐2‐enone and other alkylcyclohex‐2‐enones 7 also give naphthalenones 8 , albeit in lower yields, the major products being bicyclo[4.2.0]octan‐2‐ones (Scheme 4). No product derived from such a 1,6‐cyclization is observed in the irradiation of 3‐alkynylcyclohex‐2‐enone 9 in the presence of 2 (Scheme 4). Irradiation of the 2‐cyano‐substituted cyclohexenone 12 under these conditions again affords only traces of naphthalenone 13 , the main product now being the substituted bicyclo[4.2.0]oct‐7‐ene 16 (Scheme 5), resulting from [2+2] cycloaddition of the acetylenic C−C bond of 2 to excited 12 .     

Synthesis and Reactions of 2‐[1‐Methyl‐1‐(pyrrolidin‐2‐yl)ethyl]‐1H‐pyrrole and Some Derivatives with Aldehydes: Chiral Structures Combining a Secondary‐Amine Group with an 1H‐Pyrrole Moiety as Excellent H‐Bond Donor

The synthesis of compound 2 and its derivatives 6 and 8 combining a pyrrolidine ring with an 1H‐pyrrole unit is described (Scheme 2). Their attempted usability as organocatalysts was not successful. Reacting these simple pyrrolidine derivatives with cinnamaldehyde led to the tricyclic products 3b, 9b , and 10b first (Scheme 1, Fig. 2). The final, major products were the pyrrolo‐indolizidine tricycles 3a, 9a , and 10a obtained via the iminium ion reacting intramolecularly with the nucleophilic β‐position of the 1H‐pyrrole moiety (cf. Scheme 1).     

Herstellung neuer polycyclischer Verbindungen durch intramolekulare Diels-Alder-Reaktionen von Cyclohexa-2,4-dien-1-on-Abkömmlingen

Synthesis of new polycyclic compounds by means of intramolecular Diels-Alder reactions of cyclohexa-2,4-dien-1-one derivatives Thermal rearrangement of mesityl penta-2,4-dienyl ether ( 1 ), consisting of the isomers E (93%) and Z (7%), furnished, besides mesitol, the two mesityl penta-1,3-dienyl ethers 2 (24%) and 3 (3%), and the two tricyclic ketones 4 (4,5%) and 5 (12,5%) (Scheme 1). A probable mechanism for this formation of 2 involves a [1,5]-hydrogen shift in (Z)- 1 . Isomerisation of (E)- 1 to (Z)- 1 at 145° occurs via reversible sigmatropic [3,3]- and [5,5]-rearrangements of (E)- 1 to the cyclohexadienones 38 and 39 respectively (see Chapter A p. 1710, and Scheme 15). Formation of 3 from either (Z)- 1 or 2 is rationalized by a series of pericyclic reactions as outlined in Chapter A and Scheme 16. The tricyclic ketones 4 and 5 are undoubtedly formed by internal Diels-Alder reactions of the 6-pentadienyl-cyclohexa-2,4-dien-1-one 6 (Scheme 2). In fact, at 80° 6 is converted into 4 (5%) and 5 (35%). At 80° the cyclohexadienone derivative 7 furnished the corresponding tricyclic ketones 8 (15%) and 9 (44%) (Scheme 2). 5 and 9 contain a homotwistane skeleton. 8 and 9 are easily prepared by reaction of sodium 2,6-dimethylphenolate with 3-methyl-penta-2,4-dienyl bromide at ambient temperature, followed by heating, and finally separation by cristallization and chromatography. The cyclohexadienones 6 and 7 have mainly (E)-configuration. Here too (E) → (Z) isomerization is a prerequisite for the internal Diels-Alder reaction, and this partly takes place intramolecularly through reversible Claisen and Cope rearrangements (Scheme 17). On the other hand, experiments in the presence of 3,5-d₂-mesitol have shown (Table 1) that intermolecular reactions, involving radicals and/or ions, are also operating (see Chapter B , p. 1712). Two different modi (I and II) exist for intramolecular Diels-Alder reactions (Scheme 18). Whereas only modus I is observed in the cyclization of 5-alkenyl-cyclohexa-l,3-dienes, in that of (2)-cyclohexadienones 6 and 7 (Scheme 2) both modi are operating. Only in modus 11-type transitions is the butadienyl conjugation of the side chain retained, so that modus 11-type addition is preferred (Chapter C p. 1716). Analogously to the synthesis of the tricyclic ketones 4 , 5 , 8 and 9 , the tricyclic ketone 15 (Scheme 4) and the tetracyclic ketone 11 (Scheme 3) are prepared from mesitol, pentenyl bromide and cycloheptadienyl bromide, respectively. From the polycyclic ketones derivatives such as the alcohols 16 , 17 , 18 , 19 , 23 , 24 and 25 (Schemes 9 and 11), policyclic ethers 20 , 21 , 22 and 26 (Scheme 10), epoxides 30 , 32 (Scheme 13), diketones 31 , 33 (Scheme 13) and ether-alcohols 35 and 36 (Scheme 14) have been prepared. Most of these conversions show high stereoselectivity.     

Derivatives from Isoselenocyanates: Synthesis of 2‐Phenyl‐6H‐[5,1,3]benzoselenadiazocine

The reaction of N‐phenylbenzimidoyl isoselenocyanates 8 with primary and secondary amines in acetone at room temperature, followed by treatment with a base, led to 6H‐[5,1,3]benzoselenadiazocine derivatives of type 10 (Scheme 3). An analogous cyclization was observed when 8a and 8b were reacted with the Na salt of diethyl malonate in EtOH at room temperature, which yielded the eight‐membered selenaheterocycles 11 (Scheme 5). The molecular structures of some of the products, as well as that of a sulfur analogue, have been established by X‐ray crystallography (Figs. 1–4). The isoselenocyanates 8 have been prepared from N‐(2‐methylphenyl)benzamides 5 in a three‐step procedure via the corresponding imidoyl chlorides 6 , side‐chain chlorination to give 7 , and treatment with KSeCN (Scheme 2).     

3-Alkyl-1-benzoxepin-5-on-Derivate und 2-Alkyl-1, 4-naphthochinone aus 2-Acylaryl-propargyläthern

3-Alkyl-1-benzoxepin-5-one derivatives and 2-alkyl-1,4-naphtoquinones from 2-acylaryl propargyl ethers. It was found that 3-alkyl-1-benzoxepin-5(2H)-ones of type B can be synthesized by treating 2-acylaryl propargyl ethers of type A with sodium methylsulfinyl methide (NaMSM, dimesyl sodium) (Scheme 13). Oxepinone derivatives of type B undergo ring contraction with base (also NaMSM) to yield the quinol derivatives C which, oxidize (during work-up), if R² = H, to the 1,4-naphthoquinones D (Scheme 13). The propargyl ethers used are listed in Scheme 1. The naphthalene derivatives 1 and 3 give oxepinones (E- 9 and a mixture of 14/15 respectively), whereas the expected oxepinone from 2 is transformed directly into the quinone 11 (Scheme 2, 3 and 5). Isomerizations of 2-acetylphenyl propargyl ethers ( 4, 5 and 6 ) (Schemes 6, 7 and 8) are less successful because of side reactions. If however the acetyl group is replaced by a propionyl or substituted propionyl group (as in ethers 7 and 8 ) oxepinones are obtained again in good yield (Scheme 9). The mechanistic pathway for the transformation of naphthyl propargyl ethers (and phenyl derivatives) under influence of NaMSM is shown in Scheme 10. The base-catalysed conversion of 4-phenyl-l-benzoxepin-5(2H)-one,benzo[f]furo[2,3-c](10 H)-oxepin-4-oncsand 3-methoxy-G,11- dihydro-dibenzo[b, e]loxepin-11-oneinto thc corresponding quinones has been reported [13] [20] [21]. The conversion of 2-acylaryl propargyl others via the isolable benzoxepin-5-one derivativcs or directly into the specifically substituted 1,4-naphthoquinone derivatives is of synthetic interest.     

The Synthesis of Epiboxidine and Related Analogues as Potential Pharmacological Agents

Methyl epiboxidine‐N‐carboxylate ( 8 ) was synthesized from 7 under reductive Heck conditions (Scheme 2). The C? C coupling of the new epiboxidine analog 9 with aryl and heteroaryl halides gave by hydroarylation C‐aryl, N‐(3‐methylisoxazol‐5‐yl)‐substituted tricyclic imides 10a – 10f (Table). The [3+2] cycloaddition of 9 with nitrile oxides yielded the bridged dihydroisoxazole derivatives 11a – 11d with potential biological activity (Scheme 4).     

Synthesis of the 6-C-Methyl and 6-C-(Hydroxymethyl) Analogues of N-Acetylneuraminic Acid and of N-Acetyl-2,3-didehydro-2-deoxyneuraminic Acid

The synthesis of 6-C-methyl-Neu2en5Ac ( 4 ), 6-C-(hydroxymethyl)-Neu2en5Ac ( 5 ), and 6-C-methyl-Neu5Ac ( 6 ) is described. The 4-methylumbellyferyl glycosides 8 and 9 were also prepared but proved unstable. Protection of the previously reported nitro ether 10 (→ 11 ) followed by a Kornblum reaction gave the branched-chain derivative 13 which was transformed into aldehyde 14 and hence via 16 into the-protected 6-C-hydroxymethylated 20 and into the 6-C-methyl-substituted 18 (Scheme 1). Debenzylidenation of 20 and 18 afforded the diols 21 and 19 , respectively. Selective oxydation of 19 followed by esterification (→ 22 ), acetylation (→ 23 ), and elimination led to the protected 6-C-methyl-Neu2en5Ac derivative 24 (Scheme 2). Bromomethoxylation yielded mainly 25 and some 26 , which were reductively debrominated to 27 and 28 , respectively. Attempted deprotection of 27 did not lead to the corresponding acid, but to the 2,7- and 2,8-anhydro compounds 29 and 30 which were characterised as their peracetylated esters 31 and 32 (Scheme 3). The structure of 32 was established by X-ray analysis. Oxydation of 19 and 21 , followed by deprotection, esterification, and acetylation gave 37 and 38 , respectively (Scheme 4). The branched-chain Neu2en5Ac derivatives 4 and 5 were obtained by β-elimination (→ 39 and 40 ) and deprotection. Omission of the esterification after oxydation of 33 and 34 gave the lactones 35 and 36 which were transformed into 37 and 38 , respectively. Bromoacetoxylation of 39 gave 41-43 which were reductively debrominated to 44 (from 41 and 42 ) and 45 (Scheme 5). Bromoacetoxylation of 40 yielded 46 which was debrominated to 47. Glycosidation of the glycosyl chlorides obtained from 44 and 47 led to the α -D-glycosides 48 and 49 and to the elimination products 39 and 40 , respectively (Scheme 6). Transesterification of 48 , followed by saponification gave the unstable glycoside 8 and hence 6-C-methyl-Neu5Ac ( 6 ). The unstable glycoside 9 was obtained by similar treatment of 49 but yielded 50 under acidic conditions. The branched-chain 4 and 5 were weak inhibitors of Vibrio cholera sialidase, and 8 and 9 were very poor substrates.     

Synthese von Trifluoromethyl-substituierten Schwefel-Heterocyclen unter Verwendung von 3,3,3-Trifluorobrenztraubensäure-Derivaten

Synthesis of Trifluoromethyl-Substituted Sulfur Heterocycles Using 3,3,3-Trifluoropyruvic-Acid Derivatives The reaction of methyl 3,3,3-trifluoropyruvate ( 1 ) with 2,5-dihydro-1,3,4-thiadiazoles 4a, b in benzene at 45° yielded the corresponding methyl 5-(trifluoromethyl)-1,3-oxathiolane-5-carboxylates 5a, b (Scheme 1) via a regioselective 1,3-dipolar cycloaddition of an intermediate ‘thiocarbonyl ylide’ of type 3 . With methyl pyruvate, 4a reacted similarly to give 6 in good yield. Methyl 2-diazo-3,3,3-trifluoropropanoate ( 2 ) and thiobenzophenone ( 7a ) in toluene underwent a reaction at 50°; the only product detected in the reaction mixture was thiirane 8a (Scheme 2). With the less reactive thiocarbonyl compounds 9H-xanthene-9-thione ( 7b ) and 9H-thioxanthene-9-thione ( 7c ) as well as with 1,3-thiazole-5(4H)-thione 12 , diazo compound 2 reacted only in the presence of catalytic amounts of Rh₂(OAc)₄. In the cases of 7a and 7b , thiiranes 8b and 8c , respectively, were the sole products (Scheme 3). The crystal struture of 8c has been established by X-ray crystallography (Fig.). In the reaction with 12 , desulfurization of the primarily formed thiirane 14 gave the methyl 3,3,3-trifluoro-2-(4,5-dihydro-1,3-thiazol-5-ylidene)propanoates (E)-and (Z)- 15 (Scheme 4). A mechanism of the Rh-catalyzed reaction via a carbene addition to the thiocarbonyl S-atom is proposed in Scheme 5.     

Synthesis of 4‐(Phenylamino)quinazoline‐2(1H)‐selones and Diselenides from Isoselenocyanates: Dimroth Rearrangement of an Intermediate

The reaction of anthranilonitriles 8 with phenyl isoselenocyanates ( 1a ) in dry pyridine under reflux gave 4‐(phenylamino)quinazoline‐2(1H)‐selones 9 (Scheme 2). They are easily oxidized and converted to diselenides of type 11 . The analogous reaction of 8a with phenyl isothiocyanate ( 1b ) yielded the quinazoline‐2(1H)‐thione 10 (Scheme 2). A reaction mechanism via a Dimroth rearrangement of the primarily formed intermediate is presented in Scheme 3. The molecular structures of 10 and 11a have been established by X‐ray crystallography. Unexpectedly, no selone or diselenide was obtained in the case of the reaction with 3‐aminobenzo[b]furan‐2‐carbonitrile ( 14 ). The only product isolated was the selenide 16 (Scheme 4), the structure of which has been established by X‐ray crystallography.     

Reactions of Tricyclic Vinylcyclopropanes with Metal Carbonyls

Irradiation of the tricyclic vinylcyclopropane 3 and Fe(CO)₅ resulted in the formation of the s?,π-bonded iron complex 7 and the π,π-bonded iron complex 8 (Scheme 2). Complex 8 was easily degraded with silica gel to give hydrocarbon 9 , which reproduced 8 by photolysis in the presence of Fe(CO)₅. Photolysis of 7 afforded a mixture of 3 (23%), 9 (27,5%), and three other hydrocarbons. Oxidative degradation of 7 with ceric ammonium nitrate in methanol gave the dimethoxy-hydrocarbon 10 . - The tricyclic hydrocarbon 3 isomerized thermally to the bicyclic hydrocarbon 11 (with CH₃? C(9) in an exo position) via a homosigmatropic [1,5]-H-shift. On the other hand, 3 was converted into the other isomer 14 (with CH₃? C(9) in an endo position) by action of Mo(CO)₆ or TsOH. Both isomers 11 and 14 reacted with 4-phenyl-1,2,4-triazoline-3,5-dione to give the isomeric Diels-Alder adducts 12 and 15 , respectively, which were photochemically converted into the cage compounds 13 and 16 , respectively (Scheme 3). - Photochemical reaction of the tricyclic vinylcyclopropane 6 with Fe(CO)₅ gave the σ,π-bonded iron complexes 17 and 18 . Heating of 17 at 80° resulted in a loss of one mol of carbon monoxide to give 18 in quantitative yield. Oxidative degradation of 17 with ceric ammonium nitrate in ethanol afforded the polycyclic lactones 19 and 20 by a novel type of reaction (Scheme 4). - The tricyclic ketone 21 was thermally converted into the α,β-unsaturated ketone 22 via a homosigmatropic [1,5]-H-shift. The configuration at C(7) of 22 was confirmed to be same as that of 11 (CH₃? C(9) in an exo position) by chemical conversions: 22 was reduced with NaBH₄ to alcohol 23 which, in turn, was dehydrated with POCl₃/pyridine to 11 (Scheme 5). Reaction of ketone 21 with Mo(CO)₆ gave the α,β-unsaturated ketone 25 and a cage compound X , whose structure was not fully elucidated. - Reaction of the polycyclic epoxide 26 with Fe₂(CO)₉ or Mo(CO)₆ yielded the allyl alcohol 27 in a novel type of reaction. The epoxides 29 and 32 were similarly converted into the corresponding allyl alcohols 30 and 33 , respectively (Scheme 6).     

β-Cleavage of Potassium Bicyclo[2.2.2]oct-5-en-2-olates. Stereoselective synthesis of (±)-trichodiene

The transformations of 12 bicyclo[2.2.2]oct-5-en-2-ols ( V or VI ) to 3-(cyclohex-3-enyl)-2-alkanones ( III or IV ), via β-cleavage of their potassium alkoxides in HMPA, has been investigated (cf. Table 1). As an illustration of this synthetic methodology, a stereoselective synthesis of (±)-trichodiene ((±)- 1 ) is described which involves the β-cleavage of the tricyclic potassium alkoxides 46a and 47a to cyclopentanone 4 (cf. Scheme 7).     

A Facile and Efficient Synthesis of Arylsulfonamido‐Substituted 1,5‐Benzodiazepines and N‐[2‐(3‐Benzoylthioureido)aryl]‐3‐oxobutanamide Derivatives

A facile and efficient synthesis of 1,5‐benzodiazepines with an arylsulfonamido substituent at C(3) is described. 1,5‐Benzodiazepine, derived from the condensation of benzene‐1,2‐diamine and diketene, reacts with an arylsulfonyl isocyanate via an enamine intermediate to produce the title compounds of potential synthetic and pharmacological interest in good yields (Scheme 1). In addition, reaction of benzene‐1,2‐diamine and diketene in the presence of benzoyl isothiocyanate leads to N‐[2‐(3‐benzoylthioureido)aryl]‐3‐oxobutanamide derivatives (Scheme 2). This reaction proceeds via an imine intermediate and ring opening of diazepine. The structures were corroborated spectroscopically (IR, ¹H‐ and ¹³C‐NMR, and EI‐MS) and by elemental analyses. A plausible mechanism for this type of cyclization is proposed (Scheme 3).     

Gold(I)‐Catalyzed Cyclodehydration Enabled by the Triisopropylsilyl Group: A Synthetically Versatile Methodology

Introduction of a triisopropylsilyl group into allyl and allenyl carbinols greatly enhances the efficiency of gold(I)‐catalyzed cyclodehydration, which can provide rapid access to a library of various compounds including 1H‐indenes (Table 2 and Scheme 5), benzofulvenes (Table 3), indan‐2‐ones (Scheme 2), fulvenes (Table 4), cyclopentadienes (Table 4), 5H‐dibenzo[a,c][7]annulenes (Scheme 6) and dibenzosuberones (Scheme 6). The developed method enables unprecedented product generality for several classes of cyclodehydration reactions, which is particularly notable for the preparation of 1H‐indenes. The first synthesis of non‐benzo‐fused fulvenes via cyclodehydration of allenyl vinyl carbinols could be accomplished. The protocol is remarkable for mild conditions, operational convenience, and easy access to starting materials.     

Thermal Reaction of Azulene-1-carbaldehydes with Dimethyl Acetylenedicarboxylate

Azulene-1-carbaldehydes which have Me substituents at C(3) and C(8) and no substituent at C(6) react with excess dimethyl acetylenedicarboxylate (ADM) in decalin at 200° to yield exclusively the Diels-Alder adduct at the seven-membered ring (cf. Scheme 3). The corresponding 1-carboxylates behave similarly (Scheme 4). Azulene-1-carbaldehydes which possess no Me substituent at C(8) (e.g. 11 , 12 in Scheme 2) gave no defined products when heated with ADM in decalin. On the other hand, Me substitutents at C(2) may also assist the thermal addition of ADM at the seven-membered ring of azulene-1-carbaldehydes (Scheme 6). However, in these cases the primary tricyclic adducts react with a second molecule of ADM to yield corresponding tetracyclic compounds. The new tricyclic aldehydes 16 and 17 which were obtained in up to 50% yield (Scheme 3) could quantitatively be decarbonylated with [RhCl(PPh₃)₃] in toluene at 140° to yield a thermally equilibrated mixture of four tricycles (Scheme 8). It was found that the thermal isomerization of these tricycles occur at temperatures as low as 0° and that at temperatures > 40° the thermal equilibrium between the four tricycles is rapidly established via [1,5]-C shifts. The establishment of the equilibrium makes the existence of two further tricycles necessary (cf. Scheme 8). However, in the temperature range of up to 85° these two further tricycles could not be detected by ¹H-NMR. When heated in the presence of excess ADM in decalin at 180°, the ‘missing’ tricyclic forms could be evidenced by their tetracyclic trapping products ‘anti’- 45 and ‘anti’- 48 , respectively (Scheme 9).     

Photochemie von tricyclischen β, γ-γ′, δ′-ungesättigten Ketonen. 50. Mitteilung über Photoreaktionen

Photochemistry of tricyclic β, γ-γ′, δ′-unsaturated ketones The easily available tricyclic ketone 1 (cf. Scheme 1) with a homotwistane skeleton yielded upon direct irradiation the cyclobutanone derivative 3 by a 1,3-acyl shift. Further irradiation converted 3 into the tricyclic hydrocarbon 4 . However, acetone sensitized irradiation of 1 gave the tetracyclic ketone 5 by an oxa-di-π-methane rearrangement. Again with acetone as a sensitizer the ketone 5 was quantitatively converted to the pentacyclic ketone 6 . The conversion 5 → 6 represents a novel photochemical 1,4-acyl shift. The possible mechanisms are discussed (see Scheme 7). The tricyclic ketone 2 underwent similar types of photoreactions as 1 (Scheme 2). Unlike 5 the tetracyclic ketone 9 did not undergo a photochemical 1,4-acyl shift. The epoxides 10 and 14 derived from the ketones 1 and 2 , respectively, underwent a 1,3-acyl shift upon irradiation followed by decarbonylation, and the oxa-di-π-methane rearrangement (Schemes 3 and 4). The diketone 18 derived from 1 behaved in the same way (Scheme 5). The tetracyclic diketone 21 cyclized very easily to the internal aldol product 22 under the influence of traces of base (Scheme 5). Upon irradiation the γ, δ-unsaturated ketone 24 underwent only the Norrish type I cleavage to yield the aldehyde 25 (Scheme 6).     

Sigmatropische Umlagerungen von Aryl-propargyläthern; Synthese von 1, 5-Dimethyl-6-methylen-tricyclo[3, 2, 1, 02,7]-oct-3-en-8-on-Derivaten. Vorläufige Mitteilung

2, 6-Dimethylphenyl propargyl ether ( 10 ) and its derivatives 12–15 rearrange thermally to 1, 5-dimethyl-6-methylene-tricyclo [3.2.1.0^2,7]oct-3-en-8-one ( 9 ) and related compounds 16–19 . The ethers undergo first an aromatic [3, 3]-sigmatropic rearrangement to ortho-allenyldienones 11 , which then undergo ring closure to the tricyclic products by an electrocyclic reaction. Only in the case of the γ-methylpropargyl ether 13 , the ortho-dienone 11 is further rearranged in low yield to the para-butynylphenol 20 , but the tricyclic ketone 17 is again the main product. New data show that the known thermal cyclisation of aryl propargyl ethers to chromenes (e. g. 4 → 8 ) involves a preliminary [3, 3]-sigmatropic rearrangement.