Propellane synthesis

In Szeimies s second propellane synthesis 127 was converted to 133 by way of organometallic intermediates. Treatment with butyllithium then gave 134, which is stable to storage in the cold. ... 

Primary tritium isotope effect 849 Propellanes, synthesis of 569, 570 Protecting groups for thiols 432 acetamidomethyl 675, 676 acetyl and benzoyl 677, 678 benzyl 671, 672 benzyloxycarbonyl 678 benzylthiomethyl and phenylthio-methyl 681... 

The photocycloaddition of cyclo-olefins to cyclic aP-unsaturated ketones has been used in propellane synthesis. Thus, (837) was prepared by addition of cyclohexene to the relevant bicyclo-enone, and (838) was likewise prepared from A -octalin and... 

We ve included several papers in the References section which perform theoretical and experimental studies of the IR and Raman spectra for these compounds. These compounds were among the earliest ab initio frequency studies of such systems. In addition, in the case of propellane, theoretical predictions of its energy and structure preceded its synthesis. 

In a modified procedure the free carboxylic acid is treated with a mixture of mercuric oxide and bromine in carbon tetrachloride the otherwise necessary purification of the silver salt is thereby avoided. This procedure has been used in the first synthesis of [1.1.1 ]propellane 10. Bicyclo[l.l.l]pentane-l,3-dicarboxylic acid 8 has been converted to the dibromide 9 by the modified Hunsdiecker reaction. Treatment of 9 with t-butyllithium then resulted in a debromination and formation of the central carbon-carbon bond thus generating the propellane 10." ... 

Synthesis of the propellane (4) requires FGA. With two four-membered rings probably to be made by photochemical reactions, a carbonyl group on the six-membered ring is best, allowing a 2 + 2 disconnection. 

Two illustrations that show the power of this reaction for the preparation of strained cycloalkenes are the contractions of 102 to the propellane 103 , an application that has been reviewed , and of 104 to the bicyclo[2.1.1]hexene 105 . The utility of the Ramberg-Backlund rearrangement in the preparation of various natural products such as steroids , terpenoids and pheromones has been demonstrated. In addition to the synthetic applications mentioned in the previous subsection, several selected examples taken from the recent literature are given in equations 66-69. These examples further demonstrate the potential of this method for alkene synthesis in general. 

N-Aziridinylimines are valuable substrates for domino radical cydizations since they are able to serve simultaneously as radical acceptors and donors. They allow a versatile and general construction of quaternary carbon centers from carbonyl compounds [33]. By employing this methodology, an elegant and stereoselective synthesis of ( )-modhephene (3-70), one of the rare naturally occurring [3.3.3]propellanes,... 

The synthesis of propellanes and spirans is reviewed, attempting to explain why a starting material sometimes yields a member of one class or the other, but apparently not a mixture of both. 

The tetramesylate 11 used had been reported previously46 8. We shall see below that it nonetheless is a useful intermediate in synthesis of propellanes 8). 

Apparently Fitjer likes to work with p-TsOH in aqueous acetone. Since as of the day of the destruction of the Temple, prophecy has been withdrawn from the prophets and has been given to fools and to babes 43 I shall not prophecy but I shall hazard a prediction. I belive that there are acidic conditions, yet to be found experimentally, which will permit the synthesis of beautiful molecules, by malice aforethought, such as, say, 99, from the properly constituted derivatives of certain rotanes and their homologs. May Fitjer be successful in his quest for [m.njcoronanes but it behooves him, simultaneously, to seek optimal conditions for the preparation of, say, 99 and its propellane homologs. I would even settle for 100 or 101 ... 

For n = 1, this is the standard synthesis of [l.l.l]propellane 40a.20,21 Also for n = 3, this method makes [3.1.1]propellane 40c accessible with reasonable effort.22 Although [2.1.1]propellane 40b was detected by its IR spectrum at liquid nitrogen temperature,23 it could not be obtained as a stable compound via this route.22 The addition of halomethanes across the central bond by a radical chain mechanism is common to 40a and 40c. The addition of carbon tetrabromide to 40c afforded a 45% yield of 41.18 Likewise, a number of bicy-clo[l.l.l]pentane derivatives 42 were obtained by reaction of the corresponding halomethanes with 40a.17,24... 

The [3.3.3]propellane skeleton could also be prepared from the cyclobutene (282), which provided the product (283). The propellane (283) was an intermediate compound in the synthesis of modhephene (284) 96K... 

Y. Tobe, T. Fujii, H. Matsumoto, K. Naemura, Towards the Synthesis of Monocydic Carbon Clusters - [2+2] Cydoreversion of Propellane-Anndated Dehydroan-nulenes , Pure Appl Chem. 1996, 68,239-242. 

Chloro-2-(chloromethyl)-1-propene is commercially available but is very expensive (> 45/g for 10 g, Aldrich Chemical Company, 1996). It is commonly used in the synthesis of natural products,5 polymers,6 cryptands and crown ethers,7 compounds of biological and medical importance,8 and is the starting material for the Szeimies synthesis of [1.1.1]propellane.9... 

The synthesis of [1.1.1]propellane from 1 is essentially as reported by Michl and co-workers,10 with only a slight modification in the process of transferring the crude propellane solution. As a result of the submitters improvements in the preparation of 3-chloro-2-(chloromethy)propene4 and 1,1-dibromo-2,2-bis(chloromethyl)cyclO propane, many of the difficulties in the Szeimies route to [1.1,1]propellane have been eliminated. 

The next four procedures describe the preparation of strained ring systems. Preparation of 3-CHLORO-2-(CHLOROMETHYL)-l-PROPENE provides a facile approach to the olefin required for the synthesis of [1.1.1 [PROPELLANE, one of the most strained hydrocarbons prepared to date. The ready availability of this hydrocarbon should prove particularly useful to those interested in the development of the chemistry of this fascinating compound. Preparation of N-BENZYL-2,3-AZETIDINEDIONE provides an efficient approach to the unadorned a-keto-/3-lactam, a potential... 

The synthesis of modhephene (54), which proceeds according to plan in an overall yield of >16%, with complete control of relative stereochemistry, demonstrates the ability of radical cyclisations to form propellane systems and generate highly crowded neopentyl quaternary centres. The accepted pathway for the cyclisation of the vinyl trimethylstannane is shown in Scheme 7.25. The chair-like transition state in which the methyl substituent on the radical is pseudoequatorial, accounts for the observed endo stereoselectivity. 

Beckmann fragmentation of polycyclic structures can be of great utility and was a key step in the two synthetic routes for the synthesis of propellane 510 (equation 224). Both fragmentation processes are oxygen assisted. 

A synthesis of the 11-aryl-1 l-aza[5.3.1 ]propellan-2-one 29 was accomplished by the intermolecular cycloaddition of the cycloheptenone 26 with an aryl azide. The... 

The Wolff rearrangement has been very successfully used in the synthesis of propellanes.40 The highly strained 3-diazo[3,2.2]propellan-2-one was photolyzed in dichloromethane at — 70 °C in the presence of dimethylamine to give A W-dimethyl tricyclo[2.2.2.0 u4]octane-2-carboxamide (5), a very highly strained interesting compound with inverted geometry at the bridgehead carbons,42 in 40% yield.41... 

Cuprate conjugate additions. One step in a recent synthesis of (-t-)-modhephene (3). a natural sesquiterpene with a (3.3.3)propellane skeleton, involved conjugate addition of lithium dimethylcuprate to 1. The desired reaction proved difficult... 

The procedure described above is an improved version of the one published by Kaszynski and Michl.4 [1.1.1]Propellane is a recently reviewed7 useful precursor for the synthesis of bicyclo[1.1.1]pentanes by radical addition across the central bond, followed by further transformations of the bridgehead substituents.4 8 Under suitable conditions, one can obtain mixtures of [njstaffanes [oligomeric bicyclo[1.11 [pentanes],... 

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