Diazirines alkyl

ESR spectra, 7, 19 Diaziridinyl radicals ESR, 7, 202 reactions, 7, 19 Diazirine, alkyl-photolysis, 7, 225-226 synthesis... 

Among unsaturated C—N—N three-membered rings only the 3H-diazirines (3) are known. IH-Diazirines with a C=N double bond were never obtained. Diazirines with one or two alkyl groups at carbon were prepared in many cases, aryldiazirines only in some cases. An important role is played by difluorodiazirine as well as by diazirines containing chlorine or bromine (9). 

A further synthesis of 1-alkyl-diaziridines is the addition of Grignard compounds to the NN double bond of diazirines [Eq. (35) ]. The... 

A class of compounds which react smoothly with diazirincs are the Grignard reagents. All investigated diazirines add Grignard reagents instantly at 0 0 to the NN double bond yielding 1-alkyl-diaziridines [Eq. (62)... 

Thus the diazirines could be related by a smooth reaction to a well investigated class of compounds. The three-membered ring structure of the diazirines was thus largely confirmed. They can be obtained from compounds which certainly have a three-membered ring structure [Eq. (54)] and are easily convertible into compounds which have equally well confirmed three-membered ring structures. The structure of the 1-alkyl-diaziridines (43) obtained by the Grignard reaction were confirmed by identification with known compounds, usually prepared by the reaction of Schiff s bases with chloramine [Eq. (32)]. The results of some of these reactions are collected in Table XII. 

The 1-alkyl-diaziridines can easily be hydrolyzed to alkyl hydrazines. Hence alkyl hydrazines are easily available from Grignard reagents and thus from alkyl halides. The three last examples of Table XII show the yield of alkyl hydrazine calculated on the diazirine used. The reaction has preparative interest because the alkylation of hydrazine with alkyl halides only gives monoalkyl hydrazines in exceptional cases. ... 

Alkyl-diaziridines from Diazirines and Grignard Compounds ... 

Yield of 1-alkjd-diaziridine, calculated on the diazirine which was not isolated. A ield of the alkyl hydrazine prepared by hydrolysis of the l-alkyl-diaziridine (calculated on diazirine). 

As in experiments with diazirine 1, the maximum yields of the ylides, and hence of the carbenes, increased with increasing strength of the alkyl group s a-CH bond.56 For example, the relative yields of carbene 45 from diazoalkane photolysis were 100% for R=cyc/o-C3H5, 96% for R=t-C4H9, and 72% for R=CH3 the relative carbene yields decreased to 14% with R=C2Hs and to only 7% with R=i-C3H7. 

In general, 1,2-C shifts do not compete effectively with the 1,2-H shifts of acyclic alkyl and alkylhalocarbenes. However, r-butylchlorocarbene (18) lacks the a-H needed for a 1,2-H shift, and so affords 1,3-CH insertion and 1,2-Me migration Eq. 14. Note that only for the thermally generated 18 is the 1,2-Me shift product (26) derived from the carbene. Photolytic generation of 18 from diazirine 24 gives only 1,3-CH insertion to dimethylchlorocyclopropane 25 in this case, the 1,2-Me shift product is formed by RIES of the diazirine.27 Based on the rate constant for the 1,3-CH insertion of t-BuCCl at 25°C (9.3 x 105 s 1), we can estimate A 105 s 1 for the 1,2-Me shift at 78°C. 

Diazirines are the cyclic isomers of the alphatic diazo compounds. Both the diaziridines and the diazirines are starting materials for the synthesis of alkyl hydrazines. 3,3-Pentamethyl-enediaziridine can be hydrolyzed quantitatively to hydrazine. Methylamine may be substituted for ammonia in the procedure resulting in l-methyl-3,3-pentamethylenediaziridine (m.p. 35-36°, yield 62% of theoretical) and then methyl hydrazine. Use of ethylenediamine leads to ethylene bis-hydrazine via a bifunctional diaziridine (m.p. 143-144°, yield 48% of theoretical). Ammonia can also be replaced by w-propylamine or cydo-hexylamine cyclohexanone by acetone. 

Pentamethylenediazirine and other diazirines easily add Grignard reagents to the N—N double bond. The reaction leads to N-alkyl diaziridines which can be hydrolyzed to alkyl hydrazines. Cyclohexylhydrazine (85% yield), -propylhydrazine (88%), isopropylhydrazine (95%), and benzylhydrazine were... 

As illustrated in Section 4.1.1, the addition of nonstabihzed carbenes to the oxygen atom of a carbonyl derivative can lead to the production of carbonyl yhdes. However, these methods are not always practical for preparative scale since many side reactions can accompany the decomposition of alkyl diazo and diazirine derivatives. Landgrebe and co-worker (8) extensively studied the thermal decomposition of organomercurials in the presence of carbonyl compounds for the preparative generation of carbonyl yhdes (Scheme 4.6). 

Confirmation was provided by the observation that the species produced by the photolysis of two different carbene sources (88 and 89) in acetonitrile and by photolysis of the azirine 92 all had the same strong absorption band at 390 nm and all reacted with acrylonitrile at the same rate (fc=4.6 x 10 Af s" ). Rate constants were also measured for its reaction with a range of substituted alkenes, methanol and ferf-butanol. Laser flash photolysis work on the photolysis of 9-diazothioxan-threne in acetonitrile also produced a new band attributed the nitrile ylide 87 (47). The first alkyl-substituted example, acetonitrilio methylide (95), was produced in a similar way by the photolysis of diazomethane or diazirine in acetonitrile (20,21). This species showed a strong absorption at 280 nm and was trapped with a variety of electron-deficient olefinic and acetylenic dipolarophiles to give the expected cycloadducts (e.g., 96 and 97) in high yields. When diazomethane was used as the precursor, the reaction was carried out at —40 °C to minimize the rate of its cycloaddition to the dipolarophile. In the reactions with unsymmetrical dipolarophiles such as acrylonitrile, methyl acrylate, or methyl propiolate, the ratio of regioisomers was found to be 1 1. 

Photolysis of dialkyl- and alkyl-diazirines has been broadly investigated since the products formed gave evidence of shortlived intermediates possessing excess vibrational energy. As shown in Scheme 1 diazirines (3) were photoactivated to (235) by irradiation with a medium pressure mercury lamp with quantum yields smaller than one this means reversibly. Nitrogen extrusion yielded carbenes (236). These rearranged to the primary products, alkenes and... 

The synthesis reported by Nassal is based on the Ca-alkylation of diethyl 2-(ace-tylamino)malonate by 3-[4-(bromomethyl)phenyl]-3-(trifluoromethyl)-3//-diazirine (46) (Scheme 12) J122l The precursor for the diazirine-containing alkylating agent is 2,2,2-trifluoro-l-(4-tolyl)ethanone (39).1124 ... 

Methylhydroxycarbene, MeC(OH), has been generated in one of the three reaction pathways of the collision-induced dissociation of protonated butane-2,3-dione.13 Its enthalpy of formation was found to be 16 4 kcalmol-1. Fluorophenoxycarbene (PhOCF) has been generated inside a hydrophobic hemicarcerand (1) by irradiation of the corresponding confined diazirine.14 Its reactivity (especially dimerization and reaction with water) was significantly lowered by the incarceration, allowing its persistence for days at room temperature. New (amino)(silyl)carbenes (2) have been generated and their structure-activity relationship studied. They showed behaviour similar to those of previously reported (amino)(alkyl)carbene.15... 

Unsubstituted alkyl diazirines are ruled out because carbenes from them rearrange to olefins (Fig. 3.14). The constraints of the caged ring system do not allow this possibility with the useful adamantane diazirine, although here a fraction of the carbene is lost by intramolecular insertion (Fig. 3.15). 

In an attempt to reduce the size of the photoreactive group, Emi and Khorana (1980) investigated the properties of tetrafluorodialkyl diazirines. Unfortunately these compact molecules (Fig. 3.17) did not yield insertion products on photolysis, but rearranged internally by alkyl migration to give olefins, and underwent intramolecular insertion to yield cyclopropanes. 

An assortment of photoactivatable groups have been attached to fatty acyl chains including aryl and alkyl azides, diazirines, and diazo groups (Table 6.2). Almost all the lipids in current use contain photoactivatable... 

Scheme 4 Possible reactions of the intermediates formed after photolysis of 3-aryl-3//-diazirines. Inset shows olefin formation from carbene derivative of unsubstituted 3-alkyl-3//-diazirines via a hydride shift...

Generation of Alkyl and Cycloalkyl Carbenes - Photolysis or thermolysis of a series of alkylchlorodiazirines (16) (Scheme 7) in the presence of alkenes, such as tetramethylethene, results in 1,2-H shifts, giving the corresponding vinyl chorides (18), in competition with additions of the carbenes (17) to the alkenes, yielding cyclopropanes (19). The mechanism of these reactions is discussed in the light of results obtained from photoacoustic calorimetry, and the ratio of vinyl chloride to cyclopropane seems to depend on the excited states of the carbene precursors and also on carbene-alkene complexes. Similar reactions of related diazirines have been investigated by flash photolysis. 

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