“…First, treatment of the hydrazines with CuCl 2 resulted in oxidation to the corresponding diazetines but with anticipated formation of a complex between the diazetine and the Cu(I) ion. , Treatment of the complex with an aqueous NaOH solution released the diazetine from the complex. Published reports of similar oxidations suggested that the diazetine−Cu + complex that is formed could be easily isolated prior to release of the diazetine using NaOH. , However, we found it difficult to isolate these particular Cu + complexes and instead simply added the aqueous NaOH solution directly to the diazetine−Cu + complex in situ followed by extraction . The yields obtained ( 6a , 60%; 6b , 70%, 6c , 98%; 7 [the exo isomer of 6a ], 53%) were comparable to yields published for azo compounds in which the complex was first isolated.…”
A homologous series of tricyclic diazetines (6a-c), differing by the number of methylene groups in the saturated bridges of the fused carbon bicycles, was synthesized. The DeltaH++ of decomposition for each of the diazetines to afford N2 and the corresponding alkene was determined experimentally: 6a, 31.7; 6b, 39.3; 6c, 38.8 kcal/mol. The ground-state strain energy of each diazetine was estimated utilizing computationally obtained DeltaHf's for each of the experimentally investigated diazetines as well as several other diazetines whose DeltaH++'s had been previously reported in the literature. The sum of the ground-state strain energies and DeltaH++'s of decomposition for all of the diazetines was nearly constant, with an average value of 59 kcal/mol, suggesting that all of the diazetines decompose via the same mechanism. Generally, the higher the ground-state strain energy of the diazetine, the less the DeltaH++ for decomposition. The decomposition transition states for 6a-c and 7 were modeled computationally at the RB3LYP/6-311+G(3df,2p)//UB3LYP/6-31+G(d,p) level. The agreement of the experimentally determined DeltaH++ values with transition-state energies obtained computationally supports the reaction mechanism originally proposed by Yamabe that the elimination process occurs by an unsymmetrical, yet concerted, transition state with strong biradical character.
“…First, treatment of the hydrazines with CuCl 2 resulted in oxidation to the corresponding diazetines but with anticipated formation of a complex between the diazetine and the Cu(I) ion. , Treatment of the complex with an aqueous NaOH solution released the diazetine from the complex. Published reports of similar oxidations suggested that the diazetine−Cu + complex that is formed could be easily isolated prior to release of the diazetine using NaOH. , However, we found it difficult to isolate these particular Cu + complexes and instead simply added the aqueous NaOH solution directly to the diazetine−Cu + complex in situ followed by extraction . The yields obtained ( 6a , 60%; 6b , 70%, 6c , 98%; 7 [the exo isomer of 6a ], 53%) were comparable to yields published for azo compounds in which the complex was first isolated.…”
A homologous series of tricyclic diazetines (6a-c), differing by the number of methylene groups in the saturated bridges of the fused carbon bicycles, was synthesized. The DeltaH++ of decomposition for each of the diazetines to afford N2 and the corresponding alkene was determined experimentally: 6a, 31.7; 6b, 39.3; 6c, 38.8 kcal/mol. The ground-state strain energy of each diazetine was estimated utilizing computationally obtained DeltaHf's for each of the experimentally investigated diazetines as well as several other diazetines whose DeltaH++'s had been previously reported in the literature. The sum of the ground-state strain energies and DeltaH++'s of decomposition for all of the diazetines was nearly constant, with an average value of 59 kcal/mol, suggesting that all of the diazetines decompose via the same mechanism. Generally, the higher the ground-state strain energy of the diazetine, the less the DeltaH++ for decomposition. The decomposition transition states for 6a-c and 7 were modeled computationally at the RB3LYP/6-311+G(3df,2p)//UB3LYP/6-31+G(d,p) level. The agreement of the experimentally determined DeltaH++ values with transition-state energies obtained computationally supports the reaction mechanism originally proposed by Yamabe that the elimination process occurs by an unsymmetrical, yet concerted, transition state with strong biradical character.
“…Even though the first member of this family of compounds was described in 1962, fewer than a dozen diazetines are currently known . Despite the propensity for decomposition of diazetines to ultimately afford nitrogen and the corresponding alkene (Figure , Δ H ≈ −50 kcal/mol), diazetines are quite thermally robust (Δ H ‡ ≈ 35 kcal/mol). , This has prompted questions concerning the mechanism of decomposition of these compounds with advocacy of concerted (both [2s + 2s] and [2s + 2a] retrocycloadditions being suggested) and nonconcerted (i.e., via diradical intermediates) processes. , Detailed studies on the decomposition process have been hampered by the inaccessibility of diazetine substrates. 1a, We sought to develop a synthetic method that would be more generally applicable than traditional methods and allow for additional studies on this fascinating class of organic compounds. 1 Products from the decomposition of diazetines.…”
[reaction: see text] A novel method for the synthesis of Delta(1)-1,2-diazetines is presented. Diels-Alder cycloaddition of dienophile 4 with five dienes afforded cycloadducts in good to excellent yields. Four of the obtained cycloadducts were converted to the corresponding diazetines.
Since the discovery of the reducing properties of diborane (1939), alkali metal borohydrides (1943), and alkali metal aluminohydrides (1946) by H. I. Schlesinger, H. C. Brown, W. G. Brown, and co‐workers, considerable effort has been expended to enhance the versatility and selectivity of these widely used hydride reagents. Whereas diborane exhibits medium reaction large differences exist between sodium borohydride and lithium aluminum hydride. In contrast to the reducing action of sodium borohydride, limited originally to aldehydes, ketones, and acid chlorides, lithium aluminum hydride readily attacks almost all reducible groups. The first progress in bridging this gap in reactivity can be traced to the availability of reagents that are easily prepared by addition of Lewis acids such as boron and aluminum halides to sodium borohydride and lithium aluminum hydride; in this manner diborane, chloroaluminum hydrides, and aluminum hydride have been made accessible as reducing agents. Parallel development led to sodium alkoxyborohydrides with generally higher reactivity than the parent hydride and to alkoxyaluminum hydrides, with markedly lower reactivity and increased chemoselectivity. On the other hand, the reducing capability of sodium borohydride and lithium aluminum hydride has been enhanced by the use of metal salt–hydride systems. A large number of other complex metal hydrides have gained importance as selective reducing agents: lithium aluminum hydride–nitrogen base complexes, sodium cyanoborohydride, lithium cyanoborohydride, sulfurated sodium borohydride, zinc borohydride, diisobutylaluminum hydride, alkylaluminum compounds such as triisobutylaluminum, and tri‐
n
‐butyltin hydride. Sterically hindered organoboranes such as lithium tri‐
sec
‐butylborohydride (L‐Selectride) exhibit excellent selectivity in reduction reactions. High asymmetric induction can be achieved with some chiral organoboranes. Lithium triethylborohydride (Super‐Hydride) is a selective and exceptionally powerful reducing agent. These complex metal hydrides often provide better regio‐ and stereoselectivities than those achieved with alkoxy‐substituted hydrides; nevertheless, the alkoxyhydrides are readily available and continue to be widely used as reducing agents.
The purpose of this chapter is to present a critical review of reductions of the following compounds by metal alkoxyaluminum hydrides, alkoxyaluminum hydrides, and chiral metal alkoxyaluminohydride complexes: hydrocarbons, peroxides, ozonides, halogen compounds, unsaturated alcohols, aromatic alcohols, ethers, 1,2‐oxides, aldehydes, ketones, quinones, acetals, and ketals. The literature is covered through December 1981. Important papers that appeared through September 1982 are also reviewed. Some reactions relating to other than reducing properties of these hydrides are included for completeness. The emphasis is on the scope, limitations, and synthetic utility of the hydrides in reduction reactions and on the optimum conditions for their application as reducing agents. Currently accepted views of reaction mechanisms are discussed. Comparisons with reductions by other complex metal hydrides are limited to the most important transformations of the functional groups.
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