Solvolytic Cyclization

Cyclization, solvolytic, 54, 84 Cycloalkene oxides, 1-methyl, conversion to exocyclic methylene alcohols, 53, 20 Cyclobutadiene, generation in situ, 50, 23... 

This method for the preparation of cyclobutanone via oxaspiropentane is an adaptation of that described by Salaiin and Conia. The previously known large-scale preparations of cyclobutanone consist of the reaction of the hazardous diazomethane with ketene, the oxidative degradation or the ozonization in presence of pjrridine of methylenecyclobutane prepared from pentaerythritol, or the recently reported dithiane method of Corey and Seebach, which has the disadvantage of producing an aqueous solution of the highly water-soluble cyclobutanone. A procedure involving the solvolytic cyclization of 3-butyn-l-yl trifluoro-methanesulfonate is described in Org. Syn., 54, 84 (1974). 

Cyclization of bromostilbenes 6 to dibenz[/ ,/]oxepins 7 can be achieved by irradiation in excellent yield.102 103 Under solvolytic conditions (60% NaOH, EtOH), the yield is greatly reduced. When a silver salt (AgOAc) is used, however, complete conversion to the tricyclic system is accomplished.102 Tribenz[/>,catalyzed cyclization of biphenyl-2-yl 2 -chlorosulfonylphenyl ether in 44% yield.260... 

CYCLOBUTANONE, 51, 76 CYCLOBUTANONE VIA SOLVOLYTIC CYCLIZATION, 54, 84 Cyclobutanones, 54, 32 CYCLOBUTENE, cis-3,4-DICHLORO-,... 

The past few years have witnessed a considerable effort by several research groups to effect stereoselective syntheses of appropriately substituted hydroazulenes. Recently some new approaches to this problem have been reported. Marshall and Huffman, for instance, have found that treatment of the enone-mesylate (395) with diborane followed by base-induced fragmentation of the intermediate boronate (396) yielded the cyclodecadienol (397) in 60 % yield. Solvolysis of the p-nitrobenzoate of (397) in aqueous dioxan containing sodium bicarbonate afforded the hydroazulenol (398) in 70 % yield. The high degree of stereoselectivity in this reaction is rationalized on the basis of the preferred mode of cyclization of the allylic cation (399). To date, the solvolytic routes to hydroazulenes have... 

Butenyl halides or sulfonates cyclize under solvolytic conditions to give cyclopropyl-methyl derivatives (equation 29) when the substituents stabilize the cyclopropylmethyl... 

Silyl-substituted carbenium ions have attracted considerable experimental interest because they are believed to be intermediates in electrophilic additions to vinyl, ethynyl and aryl silanes, in solvolytic reactions and in cationic cyclization reactions1 -4,322. Despite this wide interest, knowledge concerning the effect of silyl substitution on the stabilities of carbenium ions was rather qualitative and only recently more quantitative data became available. Theoretical studies centered mainly around a- and / -silyl-substituted carbenium ions, but y-silyl effects have been also studied. 

The structure of the 2-norbomyl cation 5 is indirectly proved by the solvolytic cyclization of 2-(3-cyclopentenyl)ethanol. Thus the ar tolysis rate of nosylate 36 exceeds that of a saturated analogue by a factor of 95 This fact has been interpreted in favour of direct participation of a double bond in the substitution of an arylsulphonate anion. As shown by Sargent and Bartlett the substitution of... 

A recent synthesis of (+)-mesembrine reported by Wijnberg and Speckamp (54) utilizes an interesting solvolytically induct intramolecalar cyclization of an acetylene with an a-acylimmonium ion for the construction of the octahydroindole ring system. 

Extension of this synthetic procedure to the synthesis of the oinine alkaloid dihydromatridine was also demonstrated. An interesting sidelight in the latter synthesis was the observation that the corresponding iV-benzyl-a-acylimmonium ion (98) containing an olefinic double bond underwent solvolytic cyclization in HCO2H to give a 4 1 mixture of the formate esters... 

Interest in limonene synthase stems in part from the fact that (-)-limonene is the common precursor of menthol and carvone, respectively, of the essential oils of peppermint and spearmint species (Scheme 6) [79]. The cyclization leading to limonene is the simplest of all terpenoid cyclizations and the reaction has ample precedent in solvolytic model studies [58, 59, 80]. Thus, it is not... 

The cyclization of 318 [X = C1 or NO (References 405 and 406, respectively)] (Scheme 125) has been studied independently under free radical conditions as well as under solvolytic conditions (X = Cl). In all cases, the only product is 320 corresponding to selective (Cy5) formation under free radical conditions the yield is 85%. The cyclization of 321 (X = Cl or NO) also gives exclusively (Cy5) compounds 323 under free radical conditions. Although first reported to give the (Cy6) compound under solvolytic conditions, it has now been shown that the (Cy5) compounds (323) are also obtained from 321 under these conditions. The carboxamido and acetamido radicals... 

The facility of the solvolytic cyclizations of cyclodecadienyl / -nitro-benzoates (87, 88, and 89) is of interest even though the position of the methyl group on the transannular double bond directs the cyclizations to transfused perhydroazulenic products 143, 144). The rate of acetolysis of the 2,6-dimethyl compound (89) was estimated to be 10 — 10 times faster than trans-3- enieu-2-y / -nitrobenzoate, indicating a substantial degree of anchimeric assistance by the transannular double bond 144). 

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