PERHYDRO-9b-BORAPHENALENE

Rings of five, six, or seven members can be formed in this way. Similar cyclization can also be accomplished with other monoalkylboranes and, in some instances, with BH3 itself.384 One example is the formation of 9-BBN, shown above. Another is conversion of 1,5,9-cyclododecatriene to perhydro-9b-boraphenalene 385... 

It is essential to heat the initially formed product to 200°C to achieve isomerization of the other isomers present to cis, tran.v-perhydro-9b-boraphenalene. When this thermal treatment is omitted, the desired product is contaminated with one major (30-40%) and several minor, unidentified, isomeric substances. 

Preparation of the two stereoisomers of perhydro-9b-boraphenalene was originally reported by Koster and Rotermund,6 and the present procedure (part A) is largely based on the procedure described by these authors. However, the original stereochemical assignment was incorrect and has been reversed.3 7 Furthermore, these authors did not use the thermal treatment described above, which appears essential to achieve isomerization of other constitutional isomers into perhydro-9b-boraphe-nalene.3 The original procedure for isomerization of the cis,trans isomer to the all cis isomer has been satisfactory. Contrary to the claim made by these authors,6 however, this isomerization does not lead quantitatively to the all cis isomer, but reaches an equilibrium, which consists of the all cis and cis,trans isomers in the ratio of 88 12 this ratio was also confirmed by reverse isomerization of the pure all cis isomer.5... 

PENTYLBENZOYL CHLORIDE, 61, 8 Perhydro-9b-azaphenalene, 61, 103 PERHYDRO-9b-BORAPHENALENE, 61,... 

A practical synthesis of 1,3-OX AZEPINES VIA PHOTOISOMERIZATION OF HETERO AROMATIC V-OXIDES is illustrated for 3,1-BENZOXAZEPINE. A hydroboration procedure for the synthesis of PERHYDRO-9b-BORAPHENALENE AND PERHYDRO-9b-PHEN-ALENOL illustrates beautifully the power of this methodology in the construction of polycyclic substances. The conversion of LIMONENE TO p-MENTH-8-EN-YL METHYL ETHER demonstrates a regio-and chemoselective method for the PHOTOPROTONATION OF CYCLOALKENES. An efficient method for the conversion of a ketone to an olefin involves REDUCTIVE CLEAVAGE OF VINYL PHOSPHATES. A mild method for the conversion of a ketone into the corresponding trimethylsiloxy enol ether using trimethylsilyl acetate is shownforthe synthesis of (Z)-3-TRIMETHYLSILOXY-2-PENTENE. 

The crude product is diluted with a small amount of dry THF and the solution transferred to a 100-mL distillation flask Distillation through a 12-cm Vigreux column gives 58 0-60 1 g (66-68% yield) of a mixture of cis,trans- and as,cis-perhydro-9b-boraphenalene, bp 113-114°C (9 5 mm), H NMR (CDClj) 8 0 7 2 2... 

Carbonylation of a s,cis,/rans-perhydro-9b-boraphenalene (7) provides the c/s,cw,rrans-alcohol (8) in 70% yield.3 Presumably each transfer of a bond from... 

Preparation. The reaction of trans,trans,trans-cyc ododccatncnc (1) with triethylamine borane at 140° in perhydrocumene gives m,ct s,fra/ti-perhydro-9b-boraphenalene (2) in 73% yield.1-2... 

Two isomers of perhydro-9b-boraphenalene are known a//-c -perbydro-9b-borapbenalene (3a) and CM,tra 5-perbydro-9b-borapbenalene (3h). In tbe molecules of (3a) and (3h) tbe boron atom is imbedded in tbe center of a relatively rigid symmetrical circle of carbon atoms. Up to 1995 there are no conformational or structural studies of these interesting molecules. Nevertheless, taking into account the trigonal planar nature of the trivalent boron atom, approximate conformations of cis,cis- and CM,tra 5-perhydro-9b-boraphenalenes are shown in Scheme 8. 

Table 1 Physicochemical properties of perhydro-9b-boraphenalenes and their complexes.

Perhydro-9b-boraphenalenes (3a,b) were prepared for the first time by Koster in 1957 by hydro-boration of 1,5,9-dodecatriene <57AG684>. However, the original stereochemical assignment has been reinvestigated. Roster s Centrobor I was proved to be cw,rran5-perhydro-9b-boraphenalene (3b) and Centrobor II is the cw,cw-isomer (3a) <85JOC520>. 

It should be mentioned that c/5,cw-perhydro-9b-boraphenalene (3a) is less reactive than cisjrans-perhydro-9b-boraphenalene (3b). Thus, in contrast to (3b), (3a) does not react with water in the presence of Bu C02BEt2 up to 70 °C, remains virtually unattacked by ethylene at 150-200 °C, and reacts only slowly with hydrogen under pressure. These reactions can be used for the removal of (3b) from (3a) in a mixture <62AG329, 65LA(686)153, 74LA54>. 

Both isomers of perhydro-9b-boraphenalene (3a,b) are inert to water and probably to alcohols at ambient temperature. However in the presence of pivaloyl(diethyl)borane, c/5,n-a 5-perhydro-9b-boraphenalene (3b) reacts with water at room temperature to give anhydride, (C,2H22B)20 (29) (Equation (3)) <74LA54>. 

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