A new enantioselective synthesis of Orlistat suitable for largescale preparation is described. Therein, the first isolated key intermediate (R)-3-hexyl-5,6-dihydro-4-hydroxy-6-undecyl-2Hpyran-2-one (12) is prepared via (a) the asymmetric hydrogenation of methyl 3-oxotetradecanoate to (S)-3-hydroxytetradecanoate (9); (b) the acylation of 9 with 2-bromooctanoyl halide (bromide/chloride) to (R)-3-[(2-bromo-1-oxooctyl)oxy]-tetradecanoic acid methyl ester (11) and finally (c) the tert-butyl magnesium chloride promoted cyclization of 11 to the single enantiomer 12. The single enantiomer intermediate 12, previously published as a mixture of enantiomers 2, has been carried on through several steps to Orlistat (1) without any process changes.

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The acetone-sensitized photorearrangements of a-and cisand trans-7-methylallyl chlorides to each other and to cisand írarw-2-chloro-l-methylcyclopropane have been studied. Quenching with piperylene of the cyclopropyl chloride formation indicates that excitation transfer from triplet acetone to the allylic chlorides occurs at a rate approximately 1/100 that of transfer to piperylene, and gives a species with a quenchable lifetime of 2-3 ns which leads to the rearrangement-cyclization. Quenching of the triplet-sensitized rearrangements of Zra/ir-crotyl chloride to the cis isomer and to the allylic isomer gives similar excitation transfer rate constants with a quenchable lifetime of about 10 ns for the cis isomer production, and with a negative "lifetime" for the a isomer formation. These results are not consistent with the idea that a single quenchable intermediate leads to all of the products. The data are consistent with the idea that there are two (or more) excited-state intermediates, one of which (differing from each allylic isomer) leads to the cyclopropanes. The second intermediate may be postulated to interconnect the three allylic isomers, with its decay ratio in the absence of quencher different from its decay ratio when it interacts with quencher.The a-methylallyl chloride-7-methylallyl (crotyl) chloride system was the first one in which the photosensitized rearrangement of allylic halides to cyclopropyl halides was observed.2 The general reaction (eq 1) may be described formally as a [l,2]-sigmatropic rearrangement, accompanied (or followed) by ring closure, similar to the di-rr-methane rear-

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The photochemistry of /3-chloro-and /3-phenylcinnamyl and -crotyl chlorides has been investigated. These compounds, under both sensitized and direct irradiation, undergo cis-trans isomerizations and allylic rearrangements. The photostationary states contain substantial amounts of the thermally less stable secondary isomers. Sensitized irradiation of d-chlorocinnamyl p-toluenesulfonate and methanesulfonate also resulted in cis-trans isomerizations and rearrangements. Quantum yield and quenching results are reported and possible reaction mechanisms are discussed.