A-Diazo aldehydes

Diazocycloalkanones with five- to twelve-membered rings can be synthesized by the present procedure in good yields (Table I).4 Diazo transfer with deformylation can also be used for the preparation of bicyclic a-diazo ketones.10,11 A related procedure involving reaction of the sodium salt of an a-(hydroxy methylene)-ketone with p-toluenesulfonyl azide in ethanol has been applied to the synthesis of diazoalkyl ketones, a-diazo aldehydes, and a-diazo carboxylic esters.12... 

Allyldiethylamine behaves similarly, but the yields are low since neither the starting amine nor the products are stable to the reaction conditions. For the efficiency of the cyclopropanation of the allylic systems under discussion, a comparison can be made between the triplet-sensitized photochemical reaction and the process carried out in the presence of copper or rhodium catalysts whereas with allyl halides and allyl ethers, the transition metal catalyzed reaction often produces higher yields (especially if tetraacetatodirhodium is used), the photochemical variant is the method of choice for allyl sulfides. The catalysts react with allyl sulfides (and with allyl selenides and allylamines, for that matter) exclusively via the ylide pathway (see Section 1.2.1.2.4.2.6.3.3. and Houben-Weyl, Vol. E19b, pll30). It should also be noted that the purely thermal decomposition of dimethyl diazomalonate in allyl sulfides produces no cyclopropane, but only the ylide-derived product in high yield.Very few cyclopropanes have been synthesized by photolysis of other diazocarbonyl compounds than a-diazo esters and a-diazo ketones, although this should not be impossible in several cases (e.g. a-diazo aldehydes, a-diazocarboxamides). Irradiation of a-diazo-a-(4-nitrophenyl)acetic acid in a mixture of 2-methylbut-2-ene and methanol gave mainly l-(4-nitrophenyl)-2,2,3-trimethylcyclo-propane-1-carboxylic acid (19, 71%) in addition to some O-H insertion product (10%). ... 

Transfer of a formylcarbene unit from an a-diazo aldehyde to an alkene has never become popular. The copper-catalyzed cyclopropanation with diazoacetaldehyde to give 5 occurred in low yield, since ketene formation is competitive (for experimental procedure, see Houben-Weyl Vol.E19b, pi224). It appears that with other catalysts and at a lower temperature the cyclopropanation could be more effective. 

The reaction of chlorodimethylformiminium chloride (XXII) with diazoketones and ethyl diazoacetate gives rise to the formation of a-diazo-aldehydes XXIII ( ). In contrast, diazomethane undergoes reaction with XXII to yield 2-dimethylamino-l,3-dichloropropane ( ). 

The reaction has also been applied to compounds with other leaving groups. Diazo ketones, diazo esters, diazo nitriles, and diazo aldehydes react with trialkylboranes in a similar manner, for example. 

The mechanism is probably also similar. In this case, a base is not needed since the carbon already has an available pair of electrons. The reaction with diazo aldehydes is especially notable, since successful reactions cannot be obtained with a-halo aldehydes. ... 

Hudlicky saw in 651 an occasion to apply a-diazo ketone cyclization methodology With cyclopentene aldehyde 660 as the starting point, dienyl carboxyhc acid 661 was elaborated and transformed into d62(Scheme LXV). Cyclization, thermal isomerization, and catalytic hydrogenation gave 657 and ultimately hirsutine. 

The benzoylphenylketene generated from 321 displayed a pronounced tendency to form chemospecific [2+4] Diels-Alder adducts with the C=N group of keto-imines. When compounds 328, derived from />-aminoacetophe-none and aromatic aldehydes, were reacted with a-diazo-/3-diketone 321, 2,3-dihydro-4//-l,3-oxazin-4-ones 329 were obtained via the addition of benzoylphenylketene to the C=N bond, and no formation of the corresponding C=0 adducts, 477-l,3-dioxin-4-ones, was observed (Equation 31) <2001J(P1)2266>. 

Dauben s group utilized the same retrosynthetic disconnections, but chose to add more functionality to the cycloaddition precursor. From a simple frawi-disubstituted cyclopentane, Dauben used an aldol reaction of a cyclopropylvinyl aldehyde to prepare the cycloaddition precursor. The diazo-substituted (3-ketoester was completed using a Roskamp-Padwa coupling followed by diazo-transfer. Addition of rhodium acetate to the diazo substituted p-ketoester 179 led to an excellent 86% yield of the correct diastereomer (Scheme 4.42). 

A reaction between a-diazo ketones and a,(1-unsaturated aldehydes under rhodium(ll)-catalysis provides a route to epoxy-bridged tetrahydropyran-4-ones <2002JOC8019>. This methodology allows entry to functionalized spiro-dioxa-bridged polycyclic frameworks <2002TL3931, 2003T8117>. 

An electrochemical oxidation route to tetrahydrofuran and tetrahydropyran rings has been described, in which a silyl-substituted enol ether reacts with a regioselectivity that is reversed from the normal polarity of enol ethers (Scheme 61) <2000JA5636>. Aldol reactions of a-diazo-/ -ketoesters with aldehydes produce adducts which undergo Rh(ii)-catalyzed 0-H insertion reactions to yield highly substituted tetrahydrofurans <1997TL3837>. 

Aldehydes are efficiently converted to /3-diketo esters in 50-90 % yield by addition of ethyl diazoacetate in the presence of SnCl2 (Eq. 5). Although the reaction can be effected by a variety of Lewis acids, SnCl2, BF3, and GeCl2 are the most effective [14]. 1,3-Diketones can be prepared in 42-90 % yield by SnCl2-catalyzed reaction of a-diazo ketones with aldehydes (Eq. 6) [15]. 

Further studies on a-diazo ketones with a second more remote carbonyl group have appeared and formation of a carbonyl ylide and its addition to an added aldehyde yields bicyclic dioxolanes 199 (Scheme 19) <2004TL6485, 2005ARK(xi)146>. A rearrangement is clearly involved in the more complex reaction of a silyl diazo ester to give a dioxolan-4-one (Equation 66) <20020L4631>. 

Reactions of Phosphonium Ylides. - 2.3.1 Reactions with Carbonyl Compounds. This year we are able to report several variations of the traditional Wittig olefination which employ the addition of catalysts to effect the reaction. For example, Lebel et al. have reported a new salt-free process for the methyl-enation of aldehydes, in which the phosphorane is generated in situ from triphenylphosphine and a diazo precursor with either a rhodium- or rhenium-based catalyst (Scheme 6). It was found that the most effective combination of catalyst and diazo-compound were Wilkinson s catalyst [RhCl(PPh3)3] and... 

Reagents formed in situ by reaction of r-BUjZnI with organic halides add to carbonyl compounds, such mixed zincates do not transfer their f-butyl group. a-Diazo- 3-hydroxy esters are formed by treatment of diazoacetic esters with Et Zn and aldehydes at low temperature. Allylzinc species derived from allylic esters add to carbonyl compounds to give a- or y-adducts according to the nature of the latter. ... 

One of the most important improvements has been the successful reaction of 1-diazo-l-lithio-acetone with aldehydes, followed by acid-induced transformation of the a-diazo-/3-hydroxyketone thus formed into the corresponding /3-diketone with a number of R1 groups, in the presence of Rh11 acetate as catalyst (Equation (2)) 46... 

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