Harikisan R. Sonawane

Photochemical rearrangement of α-chloro-propiophenones to α-arylpropanoic acids: studies on chirality transfer and synthesis of (S)-(+)-ibuprofen and (S)-(+)-ketoprofen☆☆☆

Abstract A new single-step efficient photocchemical approach for α-arylpropanoic acids ( 4 ) from α chloro-propiophenones ( 5 ) is described. It involves carbonyl triplet excited state directed 1,2-aryl migration of the aryl group which has been found to be highly dependent upon the nature of the aryl substituent. The mode of this rearrangement is probed by the study of the photobehaviour of a set of optically active α-chloro-propiophenones. The results suggest that the nature of the carbonyl triplets (n,π * /π,π * ) plays an important role in the chirality transfer. This method finds application in the synthesis of optically active ibuprofen ( 4e ) and ketoprofen ( 26 ), though in moderate optical yields.

Synthesis of naturally-occurring (−)-Δ9(12)-Capnellene and its antipode: an application of the photo-induced vinylcyclopropane-cyclopentene rearrangement☆

Abstract Abundantly available (+)-Δ 3 -Carene, 1 has been transformed into enantiomerically pure key intermediates viz. the enones (−)- 7 and (+)- 7 , thus constituting a formal synthesis of both the enantiomers of Δ 9(12) -Capnellene.

Photoinduced vinylcyclopropane-cyclopentene rearrangement: A methodology for chiral bicyclo[3.2.0]heptenes. Formai syntheses of (±)-grandisol and naturally occurring ()-Δ9(12)-Capnellene and its antipode

Abstract The problem of achieving reaction selectivity in cis -alkyl vinylcyclopropanes in favour of their rearrangement to cyclopentenes, obviating the competing low energy process of the [1,5] (homo) sigmatropic hydrogen shift, is addressed. It has been demonstrated that the readily available bicyclo[4.1.0]heptenes derived from (+)-Δ3-carene. (1), upon photosensitized irradiation, are conveniently transformed into chiral cis -bicyclo [3.2.0]heptenes. The synthetic potential of this strategy has been demonstrated in realization of efficient formal syntheses of the important insect pheromone (±)-grandisol (2) and both the enantiomers of Δ9(12)-capnellene (3) from readily available 1, a major component of Indian turpentine oil.

A unique 1,2-shift selectivity in 2-hydroxypropiophenone dimethylacetals: generation of new methodologies for methyl-2-arylpropanoates and 1,2-carbonyl transposition

Abstract α -Hydroxydimethylacetals I have been shown to undergo two different rearrangements involving highly selective 1,2-shifts under mild conditions. When treated with Ph3P/CCl4, in the presence of pyridine, I were cleanly transformed via 1,2-aryl shifts into methyl 2-arylpropanoates, an important class of anti-inflammatory agents; a pronounced substituent effect has been observed in this rearrangement. On the other hand, treatment of I with catalytic amount of Ph3P/I2 in benzene furnished α-methoxy-α-aryl propan-2-ones in excellent yields and culminated in the development of a new methodology for 1,2-carbonyl transposition.

LIGHT-MEDIATED DIRECT TRANSFORMATION OF 2-CHLORO-PROPIOPHENONES INTO 2-ARYLPROPIONIC ACIDS

Abstract A strategy based on photochemical 1,2-aryl migration as the pivotal step allows efficient transformation of 2-chloro-propiophenones into 2-arylpropionic acids. A noticeable substituent-directed excited state control on the rearrangement process has been observed.

Photochemistry of substituted propiophenones: An interesting α-and aryl substituents effect on their photobehaviour I,II

Abstract Photochemistry of different α-substituted and phenyl-substituted propiophenones in methanol is investigated with a view to delineate the substituent effect with a special reference tu their rearrangement to α-arylpropanoic acids, an important class of nonsteroidal antiinflammatory agents. The results thus obtained bringsforth an important element of their reactivityprofile i.e. the α-chloro-substituent in combination with nuclear alkyl substituents (para>meta) favours 1,2-arylmigration leading to the synthetically useful reaction for α-arylpro panoic acids.

Stereospecific 1,2-aryl migration in 2-hydroxy alkyl aryl acetals with PPh3/CCl4. Syntheses of optically active ibuprofen and naproxen☆

Abstract Treatment of 2-hydroxy acetals (R)-(−)- 1 and (R)-(−)- 3 with PPh 3 and CCl 4 resulted in a stereospecific 1,2-aryl migration leading to the asymmetric synthesis of (R)-(−)- 2 and (R)-(−)- 4 respecuvely.

On the construction of bicyclo [m.3.0] bridged alkenes : thermal rearrangement of spirocyclic vinylcyclopropanes

Abstract A facile transformation of spirocyclic vinylcyclopropanes to titled bridged-alkenes is presented; this approach finds an application in the synthesis of natural product carbon framework of diverse nature such as that of precapnelladiene and muscone.

Photochemistry of organic multichromophoric molecules and reaction selectivity-I : reactions of (+) -4α -acetyl-2-carene

Abstract Selective photochemical transformations of two different bichromophores incorporated in a single molecule are reported.