Propellanes preparation

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. 

Let us now turn to simpler systems in which there are two, not three, structural alternatives for the potential product. Buchta and his collaborators published many papers on the preparation of spiro-compounds 4). His work stemmed primarily from his greater interest in these 4) rather than in the propellane by-products obtained in certain cases 4d >. The case was reversed for our group. Propellanes were paramount but sometimes spiro-compounds were obtained 5 K First we shall discuss a number of carbocyclic examples. 

A propellane containing, say, a six-membered ring and two four-membered ones (a [4.2.2]propellane) would presumably be easier to prepare than one with three four-membered rings. This assumption was proved amply true when the time came (1971) and a [4.2.2]propellane derivative was used to prepare compounds successively containing the [3.2.2] and the [2.2.2]propellane skeleton 6. ... 

We tried in 1968, as it turned out, unsuccessfully, to prepare a propellane having the [4.2.2] nucleus (actually it was a [4.2.2]propellene). But we were most successful in preparing the isomeric dispiran 7. None of the desired propellane was formed (see reaction scheme) ... 

In the abovementioned cases preparation of the propellanes was direct. A very nice instance exists, however, of rearrangement of a dispiran, 26, to Dewar benzenes 27 which happen to be [n.2.2]propelladienes. Silver ion (silver perchlorate at —20 °C) promotes the isomerization, as shown 10). 

Let us now discuss heterocyclic propellanes and dispirans. 8,1 l-Dioxa[4.3.3]propell-3-ene 34 was prepared (in 73% yield) by heating the tetrol 33 with KHS04 at 190-200 °C4e). This was accompanied by the bicyclic ether 35 (10% yield) but no... 

Sodium sulfide then gives products 58 and 59 of the hetero 3.3.3]propellane series no dispirans are reported. The same approach was used for preparation of the... 

Tetrathia[6.6.1]propellane 72 has been prepared 21. This is the parent of the dibenzo compound 7/just mentioned 20). The same tetrasubstituted cyclopropane 24 was used, this time simply with 1,2-ethanedithiol, under conditions of high dilution... 

Since our work on the preparation of a dispiran rather than the isomeric propellane 7>, I have lived with the feeling, alas, the feeling, by no means the certainty, that propellanes should be available from dispirans when the relative stability permits it. (Cf. Ref. 3 b). 

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 ... 

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... 

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... 

Exhaustive examples have demonstrated that 1,3-disubstituted bicyclo[l.l.l]pentanes can be conveniently prepared by radical addition to [l.l.l]propellane.39-43,47 Of particular interest is the peroxide-catalyzed [( -BuO)2, hv] addition of acetaldehyde to [1.1, l]propellane, which gives the 2 1 adduct l-acetyl-3-(1-hydroxyethyl)bicyclo[l,l.l]pentane (25) in a transformation pre-... 

The parent [1.1. l]propellane (la) is readily accessible by route (ii) in two steps from commercial materials. It can be prepared neat37 57 or, more conveniently, as a 2-3 % solution in diethyl ether4,58 or pentane48,59. Stable propellanes substituted with alkyl35,46,60,61 or aryl45 groups, as well as the thermally unstable 2,2-dichloro[ 1.1.1 ]propellane39 (lg), have also been reported (Chart 1). 

The treatment of the double bridgehead sulfide, l,3-bis(phenylthio)bicyclo[l.l.l]-pentane (15d), with lithium 4,4 -di-/-butylbi phenyl also induces reductive elimination and leads to [l.l.ljpropellane71. However, as the required bicyclo[l.l.l]pentanes 15 are most conveniently prepared from the corresponding propellanes, they do not really offer an alternative synthetic route to [1.1. IJpropellanes. They are best considered as convenient propellane storage materials37. 

One of the most interesting types of polycyclic carbon compounds prepared in recent years is the group of tricyclic substances known as propellanes. A typical example is tricyclo[3.2.2.0 -5]nonane, which sometimes is called [3.2.2]propellane, 12. The physical properties of several of these are included in Table 12-6. A quick look at formula 12 probably does not suggest any great structural difference from the bicyclic compounds we have discussed previously. However, if one tries to construct a ball-and-stick model of 12, one soon concludes that the propellanes are truly extraordinary substances in that all four carbon bonds at the bridgehead carbons extend, not to the comers of a tetrahedron, or even a distorted tetrahedron as for a cyclopropane ring, but... 

Anodic and cathodic elimination is simply the reverse of cathodic [eqn (16)] and anodic [eqn (15)] addition, respectively. Important cases are anodic bisdecarboxylation, either in the 1,2- (Corey and Casanova, 1963 Radlick et al., 1968 Westberg and Dauben, 1968) or 1,3-fashion (Vellturo and Griffin, 1966), with the preparation of Dewar benzene and dimethyl bicyclobutane-2,4-dicarboxylate as the more prominent cases [eqns (25) and (26)], and cathodic dehalo-genation of dihalides with the halogens in the 1,2- (Zavada et al., 1963), 1,3- (Casanova, 1974 Gerdil, 1970 Rifi, 1967, 1969), 1,4-(Casanova and Rogers, 1974 Wiberg et al., 1974) and 1,6- (Covitz, 1967) positions. The synthesis of bicyclobutanes (27) and [2,2,2]propellane (28) bear witness to the usefulness of this reaction type. 

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