Carbenes naphthyl

Fischer alkenylcarbene complexes undergo cyclopentannulation to alkenyl AT,AT-dimethylhydrazones (1-amino-1-azadienes) to furnish [3C+2S] substituted cyclopentenes in a regio- and diastereoselective way along with minor amounts of [4S+1C] pyrrole derivatives. Enantiopure carbene complexes derived from (-)-8-(2-naphthyl)menthol afford mixtures of trans,trans-cycloipentenes and ds,ds-cyclopentenes with excellent face selectivity [75]. The mechanism proposed for the formation of these cyclopentene derivatives is outlined in Scheme 28. The process is initiated by nucleophilic 1,2-attack of the carbon... 

Anthryl, 1-naphthyl, mesityl, and 4-quinolyl groups in 37h-k promote C/C aryl shift (see Table 2) their proclivity to migrate is far greater than expected from the electronic influence of the x-systems. This is presumably due to the intermediacy of spiro-linked benzenium betaines 30 31 , occurring in place of the carbenes otherwise encountered. The formation of phosphinic esters 42h-k is partly or completely suppressed 30). 

In arylcarbenes not only the internal bond angle but also the dihedral angle between the bond plane and the aryl plane can be bent. Photolysis of a- and /S-naphthyl-diazomethanes in a matrix gave two isomeric carbenes, which produced different ESR signals >. 

As expected, the absorption bands due to polynuclear aromatic carbenes are red-shifted as 71 conjugation is developed. For example, triplet di(l-naphthyl)carbene... 

IR bands for the both states. For example, singlet and triplet states of 2-naphthyl-(methoxycarbonyl)carbenes (NMCs, 17) show very different IR spectra (Scheme 9.4) (1590, 1625, 1640 cm for NMC and 1660 cm for NMC). Both states are observable in this case. In the singlet state, the carbomethoxy group assumes a conformation perpendicular to the naphthylcarbene plane to avoid destabilization of the empty carbenic 2p atomic orbital by the electron-withdrawing carbonyl group, while in the triplet, the methoxycarbonyl group is in the same plane to delocalize an unpaired electron. For this reason, there is a barrier between the two states and hence both of them are observable under these conditions. 

Time-Resolved IR Spectroscopy. More recently, time-resolved IR (TRIR) experiments have been used to characterize species with lifetimes of micro-and even nanoseconds. Since IR spectra provide structural information in more detail than UV, this technique will be more powerful than TRUV-vis if one can find a carbene that can be detected and studied by this technique. To date, however, only one carbene has been studied by using TRIR. The matrix IR study shows that the planar triplet and twisted singlet states of 2-naphthyl(methoxycartbonyl) carbenes (NMC, 17) show distinctly different IR bands (see Section 3.1.4). Both NMC and NMC are detected by TRIR in solution and their kinetics have been studied. Such experiments provide clear cut data for the reaction kinetics as well as energetics of both states (see Sections 4.2 and 4.3... 

The idea of bent triplet carbenes has been strengthened by the detection of the two possible geometric isomers of bent naphthyl-methylenes.41 When a-naphthyldiazomethane was irradiated at 77°K, the resulting ESR spectrum revealed two separate triplets with somewhat different D values. 

Although mostly alkoxy carbene complexes have been benzannulated, other types of carbene complexes are equally well suited. These include aryloxy carbene complexes as well as acyla-mino and thioalkylidene complexes, and even complexes with no heteroatoms, such as diaryl carbene complexes, are suitable (see below). Besides the commonly used methoxy and ethoxy carbene complexes, alkoxy carbene complexes with a longer alkyl chain have also been successfully reacted. The benzannulation of aryloxy carbene complexes has recently been studied to probe electronic effects [28a]. Aryloxy alkylidene complexes of type 21 have been used to prepare diaryl ethers 22, which constitute a common substructure in many important types of natural products [28b]. The benzannulation methodology provides an access to phenyl naphthyl ethers in yields of 60-93 % under mild conditions (Scheme 11). 

The benzannulation of naphthyl carbene complexes may be used as a direct route to functionalized phenanthrenes (Scheme 34) [37a]. While it is obvious that 1-naphthyl carbene complexes such as 87 lead to phenanthrenes 88 (see also Section 8.3.2, Scheme 19), chromium 2-naphthylcarbenes 89 offer two alternatives for annulation, giving either phenan-threne or anthracene derivatives. Generally, angular benzannulation affording phenanthrenes 90 is favored over linear benzannulation to give anthracene derivatives 91. A rationale for this regiopreference is the higher electron density at C-l compared with that at... 

C-3 of the naphthalene nucleus that controls the electrophilic ring-closure of the vinyl ketene intermediate moreover, the degree of aromaticity of the angular rings in the phenanthrene skeleton exceeds that in the anthracene analogues. This regioselectivity observed in the benzannulation of chromium carbenes is paralleled by results observed for 2-naphthyl cyclo-butenones [77] and for the palladium-catalyzed cyclocarbonylation of 2-naphthyl allyl acetates [78]. 

The cycloaddition of naphthyl carbene complexes has found application in the synthesis of biphenanthryl derivatives (see Section 8.5.1) [68c, 68d]. 

Intramolecular carbenoid and nitrenoid insertions are also quite effective for the preparation of peri-condensed heterocycles. Thus, photolysis of 1-naphthyl-1,2,3-triazoles 113 leads to bcnzo[d,e quinolines 115, possibly via carbene intermediate 114 (Scheme 55) <1987J(P1)413>. Similarly, on photolysis or thermolysis of 8-azido-l-arylazonaphtha-lenes 116 naphtho[l,8-<7, ]triazine derivatives 117 are formed along with A-aryhminobenzo[/y/]indazoles 118 (Scheme 56) <1978JOC2508, 1982JOC1996>. 

The same authors then proceeded to synthesise the corresponding azolium salt based on the l,r-binaphthyl scaffold (see Figure 5.23) [79]. The same failure to synthesise either the free carbene or transition metal carbene complexes from it was estabUshed experimentally. Electronic destabilisation by a double annulation effect from the two phenyl (naphthyl) rings on the seven-membered azolium ring systan is indeed the most likely explanation. 

Hexen 3,5-Dioxo-l-phenyl- El 9b, 1261 (Hydroxy-carben - Keton) Flydroperoxid l-(2-Naphthyl)-ethyl-E13/1, 161 (O-Ac - O-OH) Inden... 

Naphthyl(methoxycarbonyl)carbene (29) has been investigated in low temperature matrices, and in flash-photolysis experiments. " In each of these complementary studies the carbene was generated from the a-diazo ester, methyl 2-diazo-(2-naphthyl)acetate. Matrix photolysis of the precursor at 450 nm yields primarily the triplet ground-state carbene, which has been... 

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