Enantio- and Diastereoselective Additions to Aldehydes Using the Bifunctional Reagent 2-(Chloromethyl)-3-(tributylstannyl)propene:  Application to a Synthesis of the C₁₆−C₂₇ Segment of Bryostatin 1

Abstract

Reactions of the bifunctional allylstannane 2-(chloromethyl)-3-(tributylstannyl)propene with aldehydes have been examined. These generally occur in high yields using Lewis acid promoters and the products can be isolated and purified without incident. Good yields and high enantioselectivities are also realized in catalytic asymmetric allylations (CAA reactions) using the previously described BITIP catalyst system. Protection of the free hydroxyl can be accomplished without cyclization to the derived tetrahydrofuran, although this transformation is also facile. The utility of the incorporated allyl chloride functionality allows for the obvious use of such products in reactions with nucleophiles. Use of these products in a less obvious connective strategy is demonstrated in the synthesis of the C 12 -C 27 segment of bryostatin 1 where a connective, or "lynchpin", double-allylation process was employed. The β-hydroxy allyl chloride obtained from an initial chelation-controlled allylation of aldehyde 16 was converted to allylstannane 19 and applied in a second allylation reaction, thus allowing for a highly convergent synthesis of the bryostatin C ring backbone in a stereoselective fashion.

Total Synthesis of (–)‐13‐Acetoxymodhephene and (+)‐14‐Acetoxymodhephene

“…This result was quite surprising, because the facial discrimination of enone 8 was not expected to be large enough to override the stereoselectivity of the CBS reagents. Luche reduction [18] of ketone 8 confirmed this intrinsic facial discrimination by hydride addition, as allylic alcohol 14 was obtained with 10:1 ratio.…”

Synthesis, Structural Elucidation, And Biochemical Analysis of Immunoactive Glucuronosyl Diacylglycerides of Mycobacteria and Corynebacteria

“…The mixture was filtered and the filtrate concentrated to give a residue, which was taken up in boiling EtOAc (200 mL). The hot mixture was filtered, the filtrate concentrated, and the residue recrystallized (EtOAc/hexane) to give 9 (0.74 g, 38%) as colorless needles: mp 99–101 °C (lit . mp 98.5–100 °C); [α] D −1.0 ( c 1.0 in MeOH) (lit .…”

Synthesis of Substituted Benzenes and Phenols by Ring‐Closing Olefin Metathesis

“…Vinylboronic acid pinacol ester 12 b was prepared according to the reported procedure 26. Allylic metal reagents 13 a ,27 13 b ,15 13 c ,27 13 d ,28 13 e ,29 and 13 f 30 were prepared according to the reported procedures. Dess–Martin periodinane31 and activated MnO 2 32 were prepared according to the reported procedures.…”